LO. 


it  C 


EDUCATIONAL 


,  /'   '  AND  COLLEGE  TEXT-BOOKS. 

THIS  justly  popular  Series  of  Text-Books  is  noted  for  its  freshnes; 

pleteii'  .  oi  its 

manuf  >m  the 
simple 


The 


Th( 
tions. 

UNION 
ful 

The  s 
Oi 

UNION 
UNION 
UNION 


Sir  ii 

PRIM  A 

type 


/r 

Th< 

Series 

PROGR 
FIRST 

TE 

PROGR 

MI 

RuniM 

PROGK 

PROGR 

ARITI- 

NEW 

UNIVE 


EDUCATION  DEPT. 


. 

Count 

numerously  illustrated. 

Webster's  PRIMARY  SCHOOL  DICTION- 
ARY. 

Webster's  COMMON  SCHOOL  DICTION- 
ARY. 

Webster's  HIGH  SCHOOL  DICTIONARY. 

Webster's  ACADEMIC  DICTIONARY. 

Webster's  COUNTING-HOUSE  AND  FAM- 
ILY DICTIONARY. 


:er. 

lustra- 


beautiful 


fc 

.natical 


i  CONIC      ' 

TEGRAL 
.STRON- 

ETRY. 
/EYING, 


lie  and 
ich  are 


Also: 

Webster's  POCKET  DICTIONARY.  —  A 
pictorial  abridgment  of  the  quarto. 

Webster's  ARMY  AND  NAVY  DICTION- 
ARY.— By  Captain  E.  C.  Boynton, 
of  West  Point  Military  Academy. 


Ivison,  Blakeman,    Taylor  &  Co.'s  Publications. 


KERL'S    STANDARD    ENGLISH    GRAMMARS. 


For  more  of  originality,  practicality, 
are  recommended  over  others. 
KERL'S  FIRST  LESSONS  IN  GRAMMAR. 
KERL'S  COMMON  SCHOOL  GRAMMAR. 
KERL'S  COMPREHENSIVE  GRAMMAR. 

Recently  issued  ; 

KERL'S  COMPOSITION  AND  RHETORIC. — 
A  simple,  concise,  progressive, 
thorough,  and  practical  work  on  a 
new  plan. 

KERL'S   SHORTER   COURSE  IN   ENGLISH 


and  completeness.  KERL'S  GRA-IMARS 

GRAMMAR. — Designed   for   Schools 
where  only  one  text-book  is  us -d. 

We  also  publish  : 

SILL'S  NEW  SYNTHESIS  ;  or,  Elementary 
Grammar. 

SILL'S  BLANK  PARSING  BOOK. — To  ac- 
company above. 

WELLS'  (W.  H.)  SCHOOL  GRAMMAR. 

WELLS'  ELEMENTARY  GRAMMAR. 


GRAY'S    BOTANICAL    TEXT-BOOKS. 

These  standard  text-books  are  recognized  throughout  this  country  and 
Europe  as  the  most  complete  and  accurate  of  any  similar  works  published. 
They  are  more  extensively  used  than  all  others  combined. 


Gray's  "  How  PLANTS  GROW." 

Gray's  LESSONS  IN  BOTANY.  302  Draw- 
ings. 

Gray's  SCHOOL  AND  FIELD  BOOK  OF 
BOTANY. 

Gray's  MANUAL  OF  BOTANY.  20  Plates. 

Gray's  LESSONS  AND  MANUAL. 


Gray's  MANUAL  WITH  MOSSES,  &c.  Il- 
lustrated. 

Gray's  FIELD,  FOREST  AND  GARDEN 
BOTANY. 

Gray's  STRUCTURAL  AND  SYSTEMATIC 
BOTANY. 

FLORA  OF  THE  SOUTHERN  STATES. 


Gray's  BOTANIST'S  MICROSCOPE.      2  Lenses. 

WILLSON'S    HISTORIES. 

Famous  as  being  the  most  perfectly  graded  of  any  before  the  public. 


PRIMARY  AMERICAN  HISTORY. 
HISTORY  OF  THE  UNITED  STATES. 
AMERICAN  HISTORY.     School  Edition. 
OUTLINES  OF  GENERAL  HISTORY.  School 
Edition. 


Uni- 


OUTLINES OF  GENERAL  HISTORY. 

versity  Edition. 
WILLSON'S  CHART  OF  AMERICAN    HIS- 

TORY. 
PARLEY'S  UNIVERSAL  HISTORY. 


WELLS'    SCIENTIFIC    SERIES. 


NATURAL  PHILOSOPHY. 
PRINCIPLES  OF  CHEMISTRY. 
FIRST  PRINCIPLES  OF  GEOLOGY. 


FASQUELLE'S    FRENCH    COTJTSE 

Has  had  a  success  unrivaled  in  this  country,  having  passed  through  more 
than  fifty  editions,  and  is  still  the  best. 


Fasquelle's    Introductory    French 

Course. 
Fasquelle's    Larger    French    Course. 

Revised. 

Fasquelle's  Key  to  the  Above. 
Fasquelle's  Colloquial  French  Reader. 
Fasquelle's  Telemaque. 


Fasquelle's  Dumas'  Napoleon. 

Fasquelle's  Racine. 

Fasquelle's  Manual  of  French  Con- 
versation. 

Howard's  Aid  to  French  Composi- 
tion. 

Talbofs  French  Pronunciation. 


Containing  the  latest  researches  in  Physical  science,  and   their  practical      i 
application  to  every-day  life,  and  is  still  the  best. 
SCIENCE  OF  COMMON  THINGS.  Also: 

Hitchcock's  ANATOMY  AND  PHYSIOLOGY. 

Hitchcock's  ELEMENTARY  GEOLOGY. 

Eliot  &>  Storers  CHEMISTRY, 


THE 


SCIENCE  OF  COMMON  THINGS; 


FAMILIAK  EXPLANATION 


OF  THE 


FIRST  PRINCIPLES  OF  PHYSICAL  SCIENCE. 


SCHOOLS,  FAMILIES,  AND  YOUNG  STUDENTS. 


Ellustrattfc  fcntfc  numerous 


DAVID  A.  WELLS,  A.M. 


IYISON,   BLAKEMAN,   TAYLOE   &   CO. 

NEW  YORK:  CHICAGO: 

138  &  140  GKAND  ST.  183  &  135  STATE  ST. 


Entered  according  to  Act  of  Congress,  In  the  year  1857,  by 
IVISON  &  PHINNEY, 

isv  the  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the  boutlierm 
District  of  New  York. 


CONTENTS. 


PART  I. 

CHAP-TEE                        LAWS  AND  PROPERTIES  OF  MATTER.  PAS« 

I.  "What  we  Know  of  Matter,  and  How  we  Know  It         .  3 

II.  Attraction     . .  11 

III.  Weight         .                         19 

IV.  Motion 22 

PART  II. 

APPLICATION  OP  THE  LAWS  AND  PROPERTIES  OP  MATTER 
TO  THE  ARTS. 

I.  How  we  apply  Power 31 

II.  Strength  of  Materials 36 

III.  Application  of  Materials  for  Architectural  and  Structural 

Purposes 38 

IV.  Principles  of  Architecture 41 

PART  III. 

THE  LAWS  AND  PHENOMENA  OF  FLUIDS. 

I.  "Water  in  Motion  and  at  Rest 49 

II.  Specific  Gravity »        .        .  62 

III.  Capillary  Attraction 65 

IV.  The  General  Properties  of  Gaseous  and  Aeriform  Bodies  67 
V.  The  Atmosphere 69 

VI.  Atmospherical  Phenomena 74 

VII.  The  Pump  and  Barometer 97 

VIII.  Peculiarities  of  Climates  104 


IV  CONTENTS. 

PART  IV. 
SOUND. 

I.  Origin  and  Transmission  of  Sound         .        .        .        .        114 

II.  Vocal  arid  Musical  Sounds    .         .        .        .        .        .         120 

in.  Reflection  of  Sounds ,124 

PART  V. 

HEAT. 

I.  Nature  and  Origin  of  Heat  j  129 

II.  The  Sun  a  Source  of  Heat 133 

III.  Other  Sources  of  Heat  besides  the  Sun          ...  136 

IV.  How  Heat  is  Communicated 143 

V.  The  Phenomena  of  Dew 162 

VI.  Reflection,  Absorption,  and  Transmission  of  Heat          .        171 
VII.  Effects  of  Heat 176 

PART  VL 

VENTILATION  AND  WARMING,  COMBUSTION,  RESPIRATION, 
AND  NUTRITION. 

I.  "Warming  and  Ventilation     .         .        .        .        .        .        204 

II.  Combustion 220 

1IL  Respiration  and  Nutrition     ...  .  233 

PART  VII. 

LIGHT,   AND  HOW   WE  SEE. 

I.  Nature  and  Laws  of  Light 241 

II.  Structure  of  the  Eye  and  the  Phenomena  of  Vision        .        262 

PART  VIII. 

ELECTRICITY,    GALVANISM,    MAGNETISM,   AND  ELECTRO- 
MAGNETISM. 

I.  Electricity 275 

II.  Galvanism 289 

III.  Magnetism 295 

IV.  Electro-Magnetism 299 

PART  IX. 

FAMILIAR  CHEMISTRY.  303 


PREFACE. 


THE  design  of  the  present  volume  is  to  furnish  for  the 
use  of  schools  and  young  persons,  an  elementary  text-book 
on  the  first  principles  of  science.  For  this  purpose,  the 
system  of  question  and  answer,  which  for  certain  classes 
of  pupils  and  for  familiar  instruction  has  proved  emi- 
nently popular,  has  been  followed.  The  advantages  of  this 
system  are  : — first,  that  it  affords  a  most  simple  and  easy 
method  of  communicating  useful  and  practical  informa- 
tion : — second,  the  question  excites  a  feeling  of  curiosity  in 
the  mind  of  the  young  student,  which  serves  to  fix  the  sub- 
ject-matter more  strongly  in  the  memory : — and  thirdly, 
the  form  of  question  and  answer  imparts  truth  to  the  mind, 
in  a  logical  sequence  of  cause  and  effect,  and  by  showing 
how  consequents  in  sciences  are  deduced  from  antecedents, 
unconsciously  trains  and  familiarizes  the  pupil  to  think  and 
reason  according  to  the  true  spirit  of  inductive  philosophy. 

It  is  believed  that  the  questions  in  the.  present  volume 
are  simple,  practical,  and  expressed  in  the  plainest  language 
that  the  subject  allows.  Engravings  have  also  been  used 
to  illustrate  more  clearly  the  most  important  topics  treated 
of. 

As  this  work  has  been  designed  exclusively  as  an  elemen- 
tary book,  the  more  abstruse  and  difficult  departments  of 

M69927 


V  PREFACE. 

physical  science  hare  been  passed  over,  or  briefly  noticed  ; 
such  as  the  theory  and  application  of  the  mechanical  powers, 
the  polarization  of  light,  crystallography,  &c.  Those  who 
are  desirous  of  possessing  a  more  complete  and  elaborate 
work,  arranged  in  the  form  of  question  and  answer, — em- 
bracing the  whole  subjects  of  Natural  Philosophy,  Organic 
and  Inorganic  Chemistry,  the  applications  of  science  to  the 
.Industrial  Arts,  Geology,  *fcc.,  are  referred  to  a  work  by  the 
'author  of  the  present  volume,  entitled  "  Wells's  Familiar 
Science"  and  to  u  Wells's  Natural  Philosophy,"  in  both  of 
which  special  reference  is  made  to  the  application  of  the 
principles  of  physical  science  to  the  useful  arts  and  necessi- 
ties of  every-day  life. 

In  the  preparation  of  the  "  Science  of  Common  Things  " 
especial  care  has  been  taken  to  render  the  facts  and  prin- 
ciples given,  full,  complete,  and  accurate,  and  in  strict  con- 
formity with  the  very  latest  results  and  researches  of  modern 
science. 

XEW  TOEK,  May,  1857. 


SCIENCE  OF  COMMON  THINGS. 


PAET  I 

LAWS   AND  PROPERTIES  OF  MATTER. 


CHAPTER    I. 


WHAT   WE   KNOW   OF   MATTER,  AND   HOW   WE   KNOW   IT. 
1    What  is  matter  t 

"We  apply  the  term  matter  to  any  substance  which 
affects  our  senses. 

&  How  do  lee  know  that  anything  exists  f 

Because  our  senses  give  us  evidence  of  the  fact 

3  What  are  the  senses  t 

They  are  the  instruments,  or  means,  by  which  the 
mind  is  enabled  to  know  that  matter  exists  and  pos- 
sesses certain  properties. 

4  How  many  senses  are  there  f 

Five  ;  hearing,  seeing,  smelling,  tasting,  and  feeling. 

5  Wsuld  a  person  deprived  of  all  sensation,  be  conscious  of  any  mats- 
rial  existence  f 

He  would  not ;  for  all  knowledge  of  the  material 
world  is  derived  through  the  medium  of  the  senses. 

6  Is  the  impression  transmitted  to  the  mind  by  each  organ  of  sensation, 

different* 

It  is;  each  organ  of  sense  is  adapted  to  receive  a 
particular  influence  of  matter ;  and  is  designed  to  con- 


SCIENCE    OF  COMMON   THINGS. 


Properties  of  matter  Impenetrability. 


vey  to  the  mind  immediate  notice  of  some  peculiar 
action.  This  is  the  more  noticeable,  when  we  consider 
that,  however  delicate  its  structure,  each  organ  of 
sense  is  wholly  insensible  to  every  influence  except  that 
to  which  it  is  especially  adapted ;  thus,  the  eye  is  never 
affected  by  sound,  nor  the  ear  by  light. 

7  What  is  meant  by  the  term  body  ? 

Any  distinct  portion  of  matter  existing  in,  and  oc- 
cupying space. 

8  What  do  we  mean,  when  we  speak  of  "he  properties  or  qualities  of  a 
body? 

The  powers  belonging  to  the  body,  which  are  capa- 
ble oif^xfeiting* In .'oiii*  miad  certain  sensations. 

©  What  are  the  general  properties  of  matter  f 

Tlu-  ]a4ftd£al;  qualifies  of  matter  are  MAGNITUDE  or 

EXTENSION,  IMPENETBABiLlTY,  DIVISIBILITY,  POROSITY,  IN- 
ERTIA, DENSITY,  ELASTICITY,  DUCTILITY,  and  MALLEABILITY. 

10  What  is  magnitude  f 

The  property  of  occupying  space.  It  is  impossible 
to  conceive  of  a  portion  of  matter  so  minute  as  to  have 
no  magnitude. 

11  What  do  we  mean  by  the  term  size  of  a  body  ? 

The  quantity  of  space  a  body  occupies. 

13  What  is  the  surface  of  a  body  f 

The  external  limits  of  its  magnitude- 
is   What  is  the  area  of  a  body  ? 

The  quantity  of  surface. 

14  What  is  impenetrability  f 

That  quality  of  matter  which  precludes  the  possibility 
of  two  bodies  occupying  the  same  space  at  the  same 
time.  "When  bodies  are  said  to  be  impenetrable,  it  is 
therefore  meant,  that  one  cannot  pass  through  another 
without  displacing  some,  or  all,  of  the  component  parts 
of  that  other. 

There  are  many  instances  of  apparent  penetration  ;  but  in  all  those,  the 
parts  of  the  body  which  seem  to  be  penetrated  are  only  displaced.  Thus, 
if  a  needle  be  plunged  into  a  vessel  of  water,  all  the  water  which  pre- 
viously filled  the  space  into  which  the  needle  enters,  will  be  displaced ; 
and  the  level  of  the  water  will  rise  in  the  vessel  to  the  same  height  as  it 


SCIENCE   OF   COMMON   THINGS. 


Divisibility  of  matter.  Atoms.  Particles. 


would  by  pouring  in  so  much  more  water  as  would  fill  the  space  occupied 
by  the  needle. 

15  Why  witt  water,  or  any  other  liquid,  poured  into  a  funnel,  closely 
inserted  in  the  mouth  of  a  bottle,  or  decanter,  run  over  the  sides  f 

Because  the  air  filling  the  bottle,  and  having  no 
means  of  escape,  prevents  the  fluid  from  entering  the 
bottle ;  but  if  the  funnel  be  lifted  from  the  neck  of  the 
bottle  a  little,  so  as  to  afford  the  air  an  opportunity  to 
escape,  the  water  will  then  flow  into  the  bottle  in  an 
uninterrupted  stream. 

ie   What  is  the  figure  of  a  body  f 

Its  form  or  shape,  as  expressed  by  its  boundaries  or 
terminating  extremities. 

17  What  is  meant  by  the  divisibility  of  matter  t 

Its  property,  or  capability  of  being  divided. 

18  Is  matter  capable  of  being  divided  into  separate  portions  infinitely  or 
without  limit  f 

So  far  as  we  are  able  to  perceive  with  our  senses,  all 
matter  is  capable  of  being  divided  into  separate  por- 
tions without  limit;  yet  the  recent  investigations  of 
chemistry  have  proved  beyond  a  doubt,  that  there  is 
a  point  beyond  which  matter  is  no  longer  divisible. 
Such  a  portion  of  matter  as  cannot  be  divided  we  call 
an  atom. 

19  WJiai  ffien  is  an  atom  of  matter  f 

A  particle  so  minute,  as  to  admit  of  no  division. 
Atoms  are  conceived  to  be  the  first  principles  or  com- 
ponent parts  of  all  bodies. 

The  extent  to  which  matter  can  be  divided  and  yet  be  perceived  by 
the  senses,  is  wonderful. 

An  ounce  of  gold  may  be  divided  into  four  hundred  and  thirty-two 
thousand  million  parts.  Each  of  these  parts  will  retain  all  the  characters 
and  qualities  which  are  found  in  the  largest  masses'  of  metal.  It  retains 
its  solidity,  texture,  and  color;  it  resists  the  same  agents,  and  enters  into 
combination  with  the  same  substances. 

20  What  is  a  particle  of  matter  ? 

The  term  particle  is  also  used  to  express^  sra«Z£  com- 
ponent parts  of  matter,  but  is  generally  applied  to  those 
which  are  not  too  minute,  to  be  discovered  by  obser- 
vation. 

1* 


SCIENCE   OF   COMMON   THINGS. 


Pores  of  a  body.  Compressibility.  Density. 


31   What  are  the  pores  of  a  body  ? 

No  two  particles  of  matter  are  supposed  to  be  in 
actual  contact  with  each  other;  and  the  openings,  or 
interstitial  spaces  between  these  particles,  are  called 
pores. 

33  What  is  the  reason  that  a  sponge,  apiece  of  tcood  or  metal,  can,  by 
pressure,  be  made  to  occupy  a  smaller  space  than  it  did  originally  f 

Because  the  particles  of  which  the  sponge,  the  piece 
of  wood  or  metal,  are  composed,  are  by  pressure 
brought  more  closely  together,  diminishing  at  the  same 
time  the  pores  and  the  space  the  body  occupies. 

33  What  then  is  compressibility  ? 

That  quality  of  matter  in  virtue  of  which  a  body 
allows  its  volume  or  size  to  be  diminished,  without 
diminishing  the  number  of  atoms  or  material  particles 
of  which  it  consists. 

34  What  reason  have  we  for  supposing  that  no  two  particles  of  matter 
are  in  absolute  contact  f 

Because  all  known  bodies,  whatever  may  be  their 
nature,  are  capable  of  having  their  dimensions  reduced 
without  diminishing  the  amount  of  matter  contained  in 
them ;  hence  the  space  by  which  the  volume  may  be 
diminished  must,  before  diminution,  consist  of  pores'. 

35  What  is  density  f 

The  proportion  of  the  quantity  of  matter  in  a  body  to 
its  magnitude.  Thus,  if  of  two  substances  one  contains 
in  a  given  space  twice  as  much  matter  as  the  other,  it 
is  said  to  be  twice  as  dense. 

36  What  connexion  is  there  between  the  density  of  a  body  and  its 
porosity  ? 

A  body  will  be  more  or  less  dense  according  as  its 
particles  are  near  to  or  remote  from  each  other ;  and 
hence  it  is  evident  that  the  greater  the  density  the  less 
the  porosity,  and  the  greater  the  porosity  the  less  the 
density. 

37  Why  do  we  caU  lead  heavy,  and  feathers  light  ? 

Because  the  amount  of  matter  contained  in  a  quan- 
tity of  lead  occupying  a  given  space  is  much  greater 
than  in  a  quantity  of  feathers  capable  of  occupying  the 


SCIENCE   OF   COMMON   THINGS.  11 

Ductility.  Malleability.  Attraction. 

much  more  dense  than  the  diamond,  yet  the  metal  is 
soft,  while  the  diamond  is  the  hardest  body  in  nature. 

56    When  is  a  body  said  to  be  ductile  ? 

When  it  is  capable  of  being  drawn  into  wire.  In 
ductile  substances  the  atoms  seem  to  have  no  more 
fixed  relation  of  position  than  in  a  liquid,  but  yet  they 
cohere  very  strongly. 

y    57   When  is  a  body  said  to  be  malkabk  f 

When  it  is  capable  of  being  hammered  or  rolled  into 
thin  plates.  Bodies  that  are  malleable  are  not  always 
ductile.  Lead  and  tin  may  be  hammered  out  into 
very  thin  plates,  but  it  is  'difficult,  or  impossible,  to 
draw  out  these  metals  into  fine  wire. 


CIIAPTEE   II.' 

ATTRACTION. 

58  What  is  attraction  ? 

It  is  the  force  manifested  by  the  mutual  approach  or 
cohesion  of  bodies. 

59  Is  all  matter  subject  to  the  power  of  attraction  ? 

All  matter  is  under  the  influence  of  attraction  in 
some  of  its  forms.  Every  particle  of  matter  attracts 
every  other  particle,  and  is  in  turn  itself  attracted. 

60  What  is  repulsion  ? 

It  is  the  force  manifest  in  the  movement  of  bodies 
from  each  other.  Thus,  if  a  piece  of  glass,  having 
been  briskly  rubbed,  with  a  silk  handkerchief,  touch 
successively  two  feathers,  these  feathers,  if  brought  to- 
gether, will  move  asunder. 

61  What  is  cohesive  attraction  f 

It  is  the  force  which  holds  together  the  atoms  of 


SCIENCE    OF    COMMON   THINGS. 


Adhesion.  Examples  of  cohesion^ | 

bodies.  Cohesion  acts  only  between  particles  of  pat- 
ter of  the  same  kind,  and  at  distances  which  are  not 
measurable,  or,  as  they  are  termed,  insensible  distaaices. 

63    What  is  adhesion  ? 

Adhesion  is  attraction  between  particles  of  matter 
of  different  kinds  acting  at  immeasurably  small  dis- 
tances only,  and  uniting  the  dissimilar  particles  into 
one  mass. 

63  Why  is  mortar  used  to  fasten  bricks  together  f 

Because  the  adhesive  attraction  between  the  particles 
of  the  brick  and  the  particles  of  mortar  is  so  strong, 
that  they  unite  to  form  one  solid  mass.  j 

64  Why  is  a  bar  of  iron  stronger  than  a  bar  of  wood  of  the  same  size  ? 

Because  the  cohesion  existing  between  the  particles 
of  iron  is  greater  than  that  existing  between  the  par- 
ticles of  wood. 

65  Why  are  the  particks  of  a  liquid  more  easily  separated  than  those 
of  a  solid  ? 

Because  the  cohesive  attraction  which  binds  together 
the  particles  of  a  liquid  is  much  less  strong  than  that 
which  binds  together  the  particles  of  a  solid. 

66  Why  will  a  small  needle,  carefully  laid  upon  the  surface  of  water, 
float  f 

Because  its  weight  is  not  sufficient  to  overcome  the 
cohesion  of  the  particles  of  water  constituting  the  sur- 
face ;  consequently,  it  cannot  pass  through  them  and 
sink. 

6*7  If  you  drop  water  and  laudanum  from  the  same  vessel  why  wiU 
sixty  drops  of  the  water  fill  the  same  measure  as  one  hundred  drops  of 
laudanum  ? 

The  cohesion  between  the  particles  of  the  two  liquids 
is  different,  being  greatest  in  the  water.  Consequently, 
the  number  of  particles  which  will  adhere  together  to 
constitute  a  drop  of  water  is  greater  than  in  the  drop 
of  laudanum. 

68   Why  is  the  prescription  of  medicine  by  drops  an  unsafe  method  f 

Because  not  only  do  drops  of  fluid  from  the  same 
vessel,  and  often  of  the  same  fluid  from  different  ves- 


SCIENCE   OF   COMMON   THINGS.  13 

Attraction  of  gravitation.  Illustrations  of  gravitation. 

jj  differ  in  size,  but  also  drops  of  the  same  fluid,  to 
the  'extent  of  a  third,  from  different  parts  of  the  lip  of 
the  same  vessel. 

69  Why  is  it  difficult  to  pour  water  from  a  vessel  which  has  not  a  pro- 
jecting lip  ? 

Because,  in  consequence  of  the  attraction  between 
the  water  and  the  sides  of  the  vessel,  the  fluid  has  a 
tendency  to  run  down  along  the  inclined  outside  of  the 
vessel,  and  not  at  once  to  fall  perpendicularly. 

7*O  |  What  is  the  attraction  of  gravitation  ? 

W<$  apply  the  term  "gravity,"  or  the  "attraction 
of  gravitation,"  to  that  tendency  which  every  particle 
of  matter  in  the  universe  has  to  approach  all  other 
matter.  Terrestrial  gravitation  is  the  attraction  of  a 
body  towards  the  centre  of  the  earth. 

T'l  In  what  respect  does  the  attraction  of  gravitation  differ  from  all  other 
attractive  forces  ? 

Because  it  is  the  common  property  of  all  bodies ; 
since  everything  to  which  we  can  attach  the  idea  of 
materiality  is  aftected  more  or  less  by  gravitation. 

7*3   Why  does  an  appk  loosened  from  the  tree  fall  to  the  ground? 

Because  the  earth  attracts  or  draws  it  to  itself. 

7*3  Since  all  bodies  are  attracted  towards  the  earth,  how  does  it  happen 
that  all  smoke  and  some  other  forms  of  matter  display  the  contrary  pheno- 
menon of  ascending  from  it  ? 

Because  the  smoke  is  lighter  than  the  air,  bulk  for 
bulk,  and  floats  upon  it.  It  is  unable  to  advance,  how- 
ever, in  the  most  minute  degree,  without  displacing  or 
thrusting  downward  portions  of  the  atmosphere  equal 
to  its  own  bulk. 

7*4:  Why  does  a  cork  pressed  beneath  the  water  rise  and  float  on  the 
turf  ace  ? 

Because  the  cork  is  lighter  than  an  equal  bulk  of 
water,  and  is  pressed  up  and  sustained  by  it  in  the 
same  manner  that  the  particles  of  smoke  are  sustained 
by  the  particles  of  air. 

7*5   Why  does  a  balloon  rise  in  the  air  ? 

Because  it  is  filled  with  a  gas  which  is  lighter,  bulk 
for  bulk,  than  the  air. 


SCIENCE   OF   COMMON   THINGS. 


All  bodies  attract  each  other.  Feather  and  the  earth. 

76  How  long  witt  smoke  continue  to  float  above  the  surface  of  the  earth  f 

Until  its  particles,  uniting,  become  heavier  than  the 
air,  when  they  descend  in  the  form  of  small  flakes  of 
soot. 

77  Why  do  bubbles  in  a  cup  of  tea  range  round  the  sides  of  the  cup  ? 

Because  the  cup  attracts  them. 

78  Why  do  att  the  little  bubbles  tend  towards  the  large  ones  f 

^  Because  the  large  bubbles  (being  the  superior  masses) 
attract  them. 

79  Why  do  the  bubbles  of  a  cup  of  tea  follow  a  tea-spoon  f 

Because  the  tea-spoon  attracts  them. 

SO  Do  all  bodies  attract  each  other  equally  f 

They  attract  each  other  with  forces  proportioned  to 
their  masses. 

8  1  A  feather  falls  to  the  ground  by  the  influence  of  the  earth's  attraction. 
Now,  as  all  bodies  attract  each  other,  does  the  feather  attract  or  draw  up  the 
earth  in  any  degree  towards  itself? 

It  does,  with  a  force  proportioned  to  its  m-ass  /  but 
as  the  mass  of  the  earth  is  infinitely  greater  than  the 
feather,  the  influence  of  the  feather  is  infinitely  small, 
and  we  are  unable  to  perceive  it. 

83  What  would  be  the  consequence  if  the  feather  did  not  attract  the 
earth  f 

If  any  portion  of  the  earth,  however  small,  failed  to 
attract  another  portion,  and  not  be  itself  attracted,  the 
axis  of  the  earth  would  le  immediately  changed,  involv- 
ing an  alteration  of  climate,  and  the  place  of  the  ocean 
in  its  bed. 

83  Why  is  it  more  dangerous  to  fall  from,  a  lofty  elevation  than  from  a 
low  one  ? 

As  the  attraction  of  the  earth  varies  inversely  with 
the  square  of  the  distance,  the  force  with  which  a  fall- 
ing body  will  strike  the  ground  will  increase  in  propor- 
tion to  the  height  from  which  it  has  fallen. 

84  In  what  direction  does  a  body,  when  not  supported,  endeavor  to  fall  ? 

In  a  line  drawn  from  its  centre  of  gravity  towards 
the  centre  of  the  earth. 

85  Is  the  attraction  of  the  earth  the  same  at  att  distances  from  its  sur- 
face or  centre  f 


SCIENCE   OF  COMMON   THINGS. 


15 


Centre  of  gravity. 


Position  in  which  a  body  can  rest. 


JVb ;  the  attraction  of  the  earth  for  a  body  varies 
inversely  with  the  square  of  its  distance  from  the  'centre. 

86  How  can  this  be  illustrated  ? 

In  the  following  manner : — If  one  body  attracts  an- 
other with  a  certain  force  at  the  distance  of  one  mile,  it 
will  attract  with  four  times  the  force  at  half  a  mile, 
nine  times  the  force  at  one-third  of  a  mile,  and  so  on  in 
like  proportion.  On  the  contrary,  it  will  attract  with 
but  one-fourth  of  the  force  at  two  miles,  one-ninth  of 
the  force  at  three  miles,  one-sixteenth  of  the  force  at 
four  miles,  and  so  on  as  the  distance  increases. 

87  What  do  we  mean  by  the  centre  of  gravity  ? 

That  point  in  a  body  about  which,  if  supported,  the 
whole  body  will  balance  itself. 

88  When  you  balance  a  rod,  a  stick,  or  any  other  body,  upon  the  finger, 
where  is  the  centre  of  gravity  of  the  stick  or  body  ? 

It  is  the  point  upon  which  the  body  will  remain  at 
rest,  or  upon  which  it  is  balanced. 

89  In  what  position  only  can  a  body  rest  ? 

Only  when  its  centre  of  gravity  is  supported ;  and 
until  this  is  accomplished  the  body  will  move,  and  con- 
tinue to  do  so,  until  it  settles  into  a  position  in  which 
the  centre  of  gravity  cannot  sink  lower. 

0O   Why  does  a  person  carrying  a  weight  upon  his  back  stoop  forward  ? 

In  order  to  bring  the  centre  of  gravity  of  his  body 
and  the  load  over  his  feet. 


Fig  1. 


fifr  2. 


16  SCIENCE  OF  COMMON   THINGS. 

Centre  of  gravity  in  man  and  animals. 

If  he  carried  the  load  in  the  position  of  A,  Fig.  1,  he  would  fall  back- 
wards, as  the  direction  of  the  centre  of  gravity  would  fall  beyond  his 
heels ;  to  bring  the  centre  of  gravity  over  his  feet,  he  assumes  the  posi- 
tion indicated  by  B,  Fig.  2. 

91  When  a  person  carries  a  load  upon  his  head,  why  is  it  necessary 
to  stand  perfectly  upright  ? 

In  order  tliat  the  centre  of  gravity  may  be  over  his 
feet.  i 

Q&   Why  does  a  person  in  rising  from  a  chair  bend  forward  ? 

When  a  person  is  sitting,  the  centre  of  gravity  is 
supported  by  the  seat ;  in  an  erect  position,  the  centre 
of  gravity  is  supported  by  the  feet /  therefore,  before 
rising  it  is  necessary  to  change  the  centre  of  gravity, 
and  by  bending  forward  we  transfer  it  from  the  chair 
to  a  point  over  the  feet. 

93  Why  does  a  quadruped,  in  walking}  never  raise  loth  feet  on  the  same 
side  simultaneously  f 

Because,  if  it  did,  the  centre  of  gravity  would  be  un- 
supported, and  the  animal  would  tend  to  fall  over. 

94  Why  is  a  large  turtle  placed  on  its  back  unable  to  move  f 

Because  the  centre  of  gravity  of  the  turtle  is,  in  this 
position,  at  the  lowest  point,  and  the  animal  is  unable 
to  change  it ;  therefore  it  is  obliged  to  remain  at  rest. 

95  WJiy  is  it  more  difficult  to  overthrow  a  body  Jiaving  a  broad  base 
than  one  resting  upon  a  narrow  basis  f 

Because  a  body  cannot  fall  over,  so  long  as  a  line 
directed  from  the  centre  of  gravity  vertically  towards 
the  surface  upon  which  the  body  rests,  falls  within  the 
figure  formed  by  the  base  of  the  body  in  question. 


SCIENCE   OF  COMMON   THINGS. 


IT 


Stability  of  buildings. 


Centre  of  gravity  in  walking. 


Hence,  tlie  broader  the  base  of  a  body,  the  more  securely 
it  will  stand. 

Thus,  in  Fig.  3,  the  line  directed  vertically  from  the  centre  of  gravity, 
G,  falls  within  the  base  of  the  body,  and  it  remains  standing ;  but  in  Fig. 
4  a  similar  line  falls  without  the  base,  and  the  body  consequently  cannot 
be  maintained  in  an  upright  position,  and  must  fall. 

96  How  long  will  a  watt  or  tower  stand  securely  ? 

So  long  as  the  perpendicular  line  drawn  through  its 
eentre  of  gravity  falls  within  its  base. 

The  celebrated  leaning  tower 
pf  Pisa,  315  feet  high,  which 
inclines  12  feet  from  a  per- 
fectly upright  position,  is  an 
example  of  this  principle.  For 
instance,  the  line  in  Fig.  5, 
falling  from  the  top  of  the 
tower  to  the  ground,  and  pass- 
ing through  the  centre  of  gra- 
vity, falls  within  the  base,  and 
the  tower  stands  securely.  If, 
however,  an  attempt  had  been 
made  to  build  the  tower  a  lit- 
tle higher,  so  that  the  perpen- 
dicular line  passing  through 
the  centre  of  gravity  would 
have  fallen  beyond  the  base, 
the  structure  could  no  longer 
have  supported  itself. 

Fig.5. 

©7*   What  is  the  advantage  of  turning  out  the  toes  when  we  walk  f 

It  increases  the  breadth  of  the  base  supporting  the 
body,  and  enables  us  to  stand  more  securely. 

98  Why  do  very  fat  people  throw  hack  their  head  and  shoulders  when 
they  walk  ? 

In  order  that  they  may  effectually  keep  the  centre 
of  gravity  of  the  body  over  the  base  formed  by  the 
soles  of  the  feet. 

99  W?cy  cannot  a  man,  standing  with  his  heels  close  to  a  perpendicular 
watt,  bend  over  sufficiently  to  pick  up  any  object  that  lies  before  him  on  the 
ground,  without  falling  ? 

Because  the  wall  prevents  him  from  throwing  part 
of  his  body  backward,  to  counterbalance  the  head  and 
that  must  project  forward. 


18  SCIENCE   OF    COMMON    THINGS. 

Eope-dancing.  How  we  learn  to  walk. 

100  What  is  the  reason  that  persons  walking  arm-in-arm  shake  and 
jostle  each  other,  unless  they  make  the  movements  of  their  feet  to  correspond, 
as  soldiers  do  in  marching  ? 

When  we  walk  at  a  moderate  rate,  the  centre  of 
gravity  comes  alternately  over  the  right  and  over  the 
left  foot.  The  body  advances,  therefore,  in  a  waving 
line;  and  unless  two  persons  walking  together  keep 
step,  the  waving  motion  of  the  two  fails  to  coincide. 

101  Where  would  the  centre  of  gravity  be  in  a  wheel  made  entirely  of 
wood  and  of  a  uniform  thickness  ? 

In  the  centre. 

1OS  Where  would  the  centre  of  gravity  be  if  a  part  of  the  rim  of  the 
same  wJieel  were  made  of  iron  f 

It  would  be  changed  to  some  point  aside  from  the 
centre  of  the  wheel. 

103  In  what  does  the  art  of  balancing  or  walking  upon  a  rope  consist? 

In  keeping  the  centre  of  gravity  in  a  line  over  the 
base  upon  which  the  body  rests. 

104  What  is  the  base  upon  which  the  human  body  rests  or  is  supported  t 

The  two  feet  and  the  space  included  between  them. 

105  Why  is  it  a  very  difficult  thing  for  children  to  learn  to  walk  ? 

In  consequence  of  the  natural  upright  position  of  the 
human  body,  it  is  constantly  necessary  to  employ  some 
exertion  to  keep  our  balance,  or  to  prevent  ourselves 
from  falling,  when  we  place  one  foot  before  the  other. 
Children,  after  they  acquire  strength  to  stand,  are 
obliged  to  acquire  this  knowledge  of  preserving  the 
balance  by  experience.  When  the  art  is  once  acquired, 
the  necessary  actions  are  performed  involuntarily. 

106  Why  do  young  quadrupeds  learn  to  walk  much  sooner  than  chil- 
dren f 

Because  a  body  is  tottering  in  proportion  to  its  great 
altitude  and  narrow  base.  A  child  has  a  body  thus 
constituted,  and  learns  to  walk  but  slowly  because  of 
this  difficulty,  (perhaps  in  ten  or  twelve  months,)  while 
the  young  of  quadrupeds,  having  a  broad  supporting 
base,  are  able  to  stand  and  move  about  almost  immedi- 
ately. 

107  Are  aU  the  limbs  of  a  tall  tree  arranged  in  such  a  manner,  that  tlie 


SCIENCE   OF   COMMON   THINGS.  10 

How  trees  grow.  Weight.  *» 

line  directed  from  the  centre  of  gravity  is  caused  to  fall  within  the  base  of  the 

tree? 

Nature  causes  the  various  limbs  to  shoot  out  and 
grow  from  the  sides  with  as  much  exactness,  in  respect 
to  keeping  the  centre  of  gravity  within  the  base,  as 
though  they  had  been  all  arranged  artificially.  Each 
limb  growsj  in  respect  to  all  the  others,  in  such  a  man- 
ner as  to  preserve  a  due  balance  between  the  whole.  / 


CHAPTEK   III. 

"WEIGHT. 
1O8   What  is  weight  f 

Weight  is  the  measure  of  the  attraction  of  gravita- 
tion, or,  in  other  words,  it  is  the  measure  of  force  with 
which  a  body^  is  attracted  by  the  earth.  Iti  an  ordi- 
nary sense  it  is  the  quantity  of  matter  contained  in  a 
body,  as  ascertained  by  the  balance. 

1O0  To  what  is  the  weight  of  a  tody  proportional  f 

The  weight  of  a  body  is  always  proportional  to  the 
quantity  of  matter  contained  in  it. 

110  Why  witt  a  ball  of  kad  weigh  more  than  a  baU  of  cotton  of  the 
same  size  ? 

Because  the  quantity  of  matter  contained  in  the  ball 
of  lead  is  much  greater  than  the  quantity  of  matter 
contained  in  the  ball  of  cotton.  The  attraction  of  gra- 
vitation being  proportioned  to  the  quantity  of  matter, 
it  follows  that  the  lead  ball  will  be  drawn  towards  the 
earth  with  a  greater  force  (i.  e.  will  weigh  more)  than 
the  ball  of  cotton. 

111  A  man  of  moderate  weight  upon  the  surface  of  the  earth  would 
weigh  two  tons  if  transported  to  the  surface  of  the  sun :  why  would  he  weigh 
more  upon  the  surface  of  the  sun  than  upon  the  surface  of  the  earth  f 


20  SCIENCE   OF  COMMON    THINGS. 

TV  hen  a  body  weighs  the  most  Systems  of  weights. 

Because  the  attractive  force  of  the  sun,  on  account 
of  its  greater  magnitude,  far  exceeds  the  attractive 
force  of  the  earth. 

11Q  Why  witt  a  mass  of  iron  weigh  less  on  the  top  of  a  high  mountain 
than  at  the  level  of  the  sea  f 

Because  the  force  of  the  earth's  attraction  is  less  at  the 
top  of  the  mountain  than  at  the  sea-level  ;  the  attrac- 
tion (and,  therefore,  the  weight  of  a  body)  being  greatest 
at  the  surface  of  the  earth,  and  decreasing  upward,  as 
the  square  of  its  distance  from  the  centre  of  the  earth 
increases. 

A  ball  of  iron,  weighing  a  thousand  pounds  at  the  level  of  the  sea, 
~y  would  be  perceived  to  have  lost  two  pounds  of  its  weight  if  taken  to  the 
top  of  a  mountain  four  miles  high,  a  spring  balance  being  used. 

113  Where  witt  a  body  weigh  the  most  on  the  surface  of  the  earth  ? 

At  the  poles  of  the  earth,  for  at  these  points  the 
attractive  power  is  greatest. 

It  must  be  remembered  that  the  earth  is  not  a  perfect  sphere,  but  flat- 
tened at  the  poles :  consequently,  the  poles  of  the  earth  are  nearer  the 
centre  of  attraction  (i.  e.  the  centre  of  the  earth)  than  any  other  point  on 
its  surface. 

114  Where  witt  a  body  weigh  the  least  on  the  earths  surface  f 

At  the  equator,  for  there  the  attractive  power  is  less  ; 
the  surface  at  this  point  being  the  most  distant  from 
the  centre  of  the  earth. 

115  What  would  be  the  weight  of  a  body  carried  to  the  centre  of  the 
earth  f 

It  would  have  no  weight ;  for  the  attraction  of  gra- 
vitation acting  equally  in  every  direction,  no  eftect 
would  be  produced ;  and  the  body  wrould  be  fixed  as 
if  sustained  by  a  number  of  magnetic  points. 

116  What  two  systems  of  weights  are  employed  in  tlie  United  States 
and  Great  Britain  f 

Troy  weight  and  avoirdupois  weight. 

117'  What  is  Troy  weight  used  for }  and  from  whence  does  it  derive  its 
name? 

Troy  weight  is  used  for  weighing  gold  and  silver. 
It  derives  its  name  from  the  ancient  designation  of 
London,  Troy  Novant,  or  from  Troyes,  in  France, 
where  it  was  first  adopted  in  Europe.  It  has  existed 
in  England  from  the  time  of  Edward  the  Confessor. 


SCIENCE   OF   COMMON   THINGS.  21 

Avoirdupois  and  grain  weights.  English,  American,  and  French  weights. 

118  What  is  avoirdupois  weight  used  for,  and  from  whence  does  it 
uerive  its  name  ? 

Avoirdupois  weight  is  used  for  the  weight  of  mer- 
chandise other  than  the  precious  metals.  It  derives  its 
name  from  the  French  avoirs  (averia\  goods  or  chat- 
tels, and  poids,  weight. 

11Q    What  is  a  grain  weight  f 

A  grain  weight  is  the  smallest  measure  of  weight 
made  use  of  in  the  English  system.  By  a  law  of  Eng- 
land enacted  in  1286,  it  was  ordered  that  32  grains 
of  wheat,  well  dried,  should  weigh  a  pennyweight. 
Hence  the  name  grain  applied  to  this  measure  of 
weight.  It  was  afterwards  ordered  that  a  pennyweight 
should  be  divided  into  only  24  grains. 

150  How  do  we  make  a  grain  weight  for  practical  purposes  f 

By  weighing  a  thin  plate  of  metal  of  uniform  thick- 
ness, and  cutting  out,  by  measurement,  such  a  propor- 
tion of  the  whole  as  should  give  one  grain.  In  this 
way,  weights  may  be  obtained  for  chemical  purposes, 
which  weigh  only  lTrVu1;h  part  of  a  grain. 

151  What  part  of  an  inch  is  a  line  f 

One-twelfth  of  an  inch  is  designated  as  a  line. 

1SS  Are  tJie  standards  of  weights  and  measures  in  the  United  States 
tlie  same  as  in  Great  Britain  ? 

They  are  essentially  the  same. 

1S3  Where  are  the  standards  of  weights  and  measures  to  be  found  in 
the  United  States  ? 

At  Washington,  and  at  the  capitals  of  the  several 
States  of  the  Union ;  sets  having  been  furnished  to 
each  State  by  the  United  States. 

124  Are  the  weights  and  measures  used  in  France  the  same  as  those  of 
the  United  States  and  England  ? 

No ;  they  are  entirely  different.  Within  a  compa- 
ratively recent  time  the  French  have  reconstructed 
their  old  system  of  weights  and  measures,  and  formed 
another  on  an  entirely  new  plan.  The  French  system 
is,  at  present,  the  best  and  most  accurate  system 
existing. 


SCIENCE  OF  COMMON  THINGS. 


Force.  Motion.  Friction. 


CHAPTER   IYc 

MOTION. 
135   What  is  force  f 

Force  is  whatever  causes  or  opposes  ike  production 
of  motion  in  matter. 

1SS   What  is  motion  f 

It  is  the  term  applied  to  the  phenomena  of  the 
changing  of  place  among  bodies. 

13  *7   What  would  be  the  state  of  things  if  no  motion  existed  f 

The  universe  would  be  dead.  There  would  be  no 
rising  and  setting  of  the  sun,  no  flow  of  water  or  of  air 
(wind),  no  sound,  light,  or  animal  existence. 

128  The  surface  of  the  earth  at  the  equator  moves  at  the  rate  of  about  a 
thousand  miles  in  an  hour :  why  are  men  not  sensible  of  this  rapid  move- 
ment  of  the  earth  f 

Because  all  objects  about  the  observer  are  moving  in 
common  with  him.  It  is  the  natural  uniformity  of  the 
undisturbed  motion  which  causes  the  earth  and  all  the 
bodies  moving  together  with  it  upon  its  surface  to  ap- 
pear at  rest. 

120  How  can  you  easily  see  that  the  earth  is  in  motion  f 

By  looking  at  some  object  that  is  entirely  uncon- 
nected with  it,  as  the  sun  or  the  stars.  We  are  here, 
however,  liable  to  the  mistake  that  the  sun  or  stars  are 
in  motion,  and  not  we  ourselves  with  the  earth. 

ISO  Does  the  sun  really  rise  and  set  each  day  ? 

The  sun  maintains  very  nearly  a  constant  position ; 
but  the  earth  revolves,  and  is  constantly  changing  its 
position.  Really,  therefore,  the  sun  neither  rises  nor 
sets. 

131  What  do  we  mean  by  the  term  friction  f 

In  mechanics,  it  signifies  the  resistance  which  a 
moving  body  meets  with  from  the  surface  on  which  it 
moves. 


SCIENCE   OF   COMMON  THINGS.  23 


Impossibility  of  perpetual  motion.  Centrifugal  force. 


132  Is  it  possible  to  construct  any  machine,  w  arrangement  of  matter^ 
which  will  perpetually  continue  in  motion  ? 

It  is  not  /  because  the  operations  of  gravity,  the  re- 
sistance of  the  medium  through  which  the  body  moves , 
or  the  friction  of  the  surfaces  upon  which  the  lody 
rests,  will,  in  a  given  time,  destroy  and  terminate  all 
motion.  In  addition  to  this,  all  materials  which  we 
employ  in  construction  will,  in  the  course  of  time,  wear 
out  by  use,  or  decay  by  natural  agencies. 

133  Do  we  know  of  any  instances  of  perpetual  motion  in  nature  1 

Yes  •  the  various  planetary  bodies  belonging  to  the 
solar  system  have  been  moving  with  undiminished 
velocity  for  ages  past ;  and,  unless  prevented  by  the 
agency  which  governs  all  nature,  will  continue  to 
move  in  the  same  manner  for  ages  to  come. 

134  Why  are  horses  obliged  to  make  a  much  greater  exertion  to  start  a 
carriage  than  afterwards  to  keep  it  in  motion  ? 

Because  when  a  carriage  is  once  put  in  motion  upon 
a  level  road,  with  a  determinate  speed,  the  only  force 
necessary  to  sustain  the  motion  is  that  which  is  suffi- 
cient to  overcome  the  friction  of  the  road  /  but,  at 
starting,  a  greater  expenditure  of  force  is  necessary, 
inasmuch  as  not  only  the  friction  is  to  be  overcome, 
but  the  force  with  which  the  vehicle  is  intended  to 
move  must  be  communicated  to  it. 

135  What  is  centrifugal  force? 

It  is  that  force  which  causes  a  revolving  body  to  fly 
from  a  centre. 

136  Why  does  a  stone,  discharged  from  a  sling,  move  forwards,  when 
the  cord  which  retained  it  is  loosened  f 

Because  of  the  centrifugal  force  it- has  acquired  by 
the  whirling  of  the  sling  previous  to  the  discharge. 

137  Why  do  grindstones  or  wheels,  in  rapid  motion,  not  unfrequenfty 
'break  and  fly  to  pieces  with  great  violence  ? 

Because  the  centrifugal  force,  generated  by  the  rapid 
revolving  motion,  overcomes  the  cohesion  of  the  parti- 
cles, and  thus  causes  them  to  separate  and  fly  from  the 
centre. 


SCIENCE   OF  COMMON   THINGS. 


Illustrations  of  centrifugal  force.  Revolution  of  the  earth. 

133  Can  almost  all  revolving  bodies  be  broken  by  sufficient  rotative 
velocity  ? 

Yes;  for  the  centrifugal  force  increases  with  the 
rapidity  of  revolution,  and  finally  becomes  too  strong 
to  be  resisted  by  the  cohesive  force  which  binds  the 
particles  of  the  body  together. 

13Q  When  a  vessel  containing  water  is  whirkd 
rapidly  round,  why  does  not  the  water  fall  out  when  the 
vessel  is  upside  down  ? 

Because  the  centrifugal  force,  tending 
to  make  the  water  fly  from  the  centre, 
overcomes  or  balances  the  attraction  of 
gravitation,  which  tends  to  cause  the 
water  to  fall  out. 

In  Fig.  6.  the  water  contained  in  the  bucket  which 
is  upside  down,  has  no  support  under  it,  and  if  the 
bucket  were  kept  still  in  its  inverted  position  for  a 
single  moment  the  water  would  fall  out  by  its  own 
weight,  or,  in  other  words,  by  the  attraction  of  gravi- 
tation :  but  the  centrifugal  force,  which  is  caused  by 
the  whirling  of  the  bucket  in  the  direction  of  the 
arrow,  tends  to  drive  the  water  out  through  the  bot- 
tom and  side  of  the  vessel,  and  as  this  last  force  is 
equal  to  and  balances  the  other,  the  water  retains  its 
place,  and  not  a  drop  is  spilled. 


How  much  faster  would  the  earth  be  required 
to  revolve  in  order  to  make  the  centrifugal  force  equal  to 
the  attraction  of  gravitation  f 

/Seventeen  times  faster,  or  in  eighty- 
four  minutes,  instead  of  twenty-four 
hours  :  in  this  case  all  bodies  at  the 
equator  of  the  earth  would  be  destitute 
of  weight. 

141  What  would  be  the  consequence  if  the  earth 
revolved  around  its  axis  in  less  time  than  eighty-four 
minutes  ? 

I     Gravitation  would  be  completely  over- 
_    powered,  and  all  fluids  and  loose  sub- 
Fi«  6-          stances  would  fly  from  the  surface. 

143   Why  does  a  man  or  horse,  in  turning  a  corner  rapidly,  incline 
inwards,  or  kan  towards  the  corner  t 

Because  the  centrifugal  force,  produced  by  turning 


SCIENCE   OF   COMMON"   THINGS. 


25 


Action  of  centrifugal  force  in  equestrian  sports. 


rapidly,  tends  to  throw  him  away  from,  the  corner  y 
therefore,  he  inclines  inwards  to  counteract  it. 

143    Why  does  a  horse  in  a  circus  ring  lean  towards  the  centre  1 

When  the  horse  moves  rapidly  around  the  circular 
course,  the  centrifugal  force  generated,  tends  to  throw 
him  over,  outwardly,  or  away  from  the  centre  of  the 
ring  ;  and  this  tendency  the  animal  counteracts,  by 
inclining  his  body  in  an  opposite  direction. 


Fig.  7. 

In  all  equestrian  feats  exhibited  in  the  circus,  it  will  be  observed  that 
not  only  the  horse  but  the  rider  inclines  his  body  towards  the  centre, 
Fig.  7,  and  according  as  the  speed  of  the  horse  round  the  ring  is  increased, 
this  inclination  becomes  more  considerable.  "When  the  horse  walks 
slowly  round  a  large  ring  this  inclination  of  his  body  is  imperceptible ;  if 
he  trot  there  is  a  visible  inclination  inwards,  and  if  he  gallop  he  inclines 
still  more,  and  when  urged  to  full  speed  he  leans  very  far  over  on  his 
side,  and  his  feet  will  be  heard  to  strike  against  the  partition  which  defines 
the  ring.  The  explanation  of  all  this  is,  that  the  centrifugal  force  caused 
by  the  rapid  motion  around  the  ring  tends  to  throw  the  horse  out  of,  and 
away  from,  the  circular  course,  and  this  he  counteracts  by  leaning 
inwards. 

144  Why  do  water-dogs  give  a  semi-rotary  movement  to  their  skin  to 
free  themselves  from  water  ? 

Because  in  this  way  a  centrifugal  force  is  generated, 
which  causes  the  drops  of  water  aaherent  to  them  to 
fly  off. 


26  SCIENCE   OF  COMMON   THINGS. 

Phenomena  of  jumping.  Flying  of  birds.  Flying  and  leaping. 

145  Why  does  a  person  who  is  about  to  leap  over  a  ditch  or  chasm  first 
make  a  run  of  a  little  distance  ? 

In  order  that  the  impetus  he  acquires  in  running 
may  help  him  in  the  jump. 

140    Why  is  a  standing  leap  always  shorter  than  a  running  one  f 

Because  in  the  running  leap,  in  addition  to  the  force 
acquired  by  the  contraction  of  the  muscles,  we  have 
added  the  force  of  the  motion  acquired  by  running. 

147  Why  do  we  kick  against  the  door-post  to  shake  the  snow  or  dust 
from  our  shoes  ? 

The  forward  motion  of  the  foot  is  arrested  by  the 
impact  against  the  post ;  but  this  is  not  the  case  with 
respect  to  the  particles  of  dust  or  snow,  which  are  not 
attached  to  the  foot ;  but  the  motion  imparted  to  them 
equally  with  the  foot  is  continued,  and  causes  them  to 
fly  off. 

148  Why  do  we  beat  a  coat  or  carpet  to  expel  the  dust  f 

The  cause  which  arrests  the  motion  imparted  to  the 
coat  or  carpet  by  the  blow  does  not  arrest  the  particles 
of  dust,  and  their  motion  being  continued,  they  fly  off. 

149  Why  can  birds  fly  f 

Because  they  have  the  largest  bones  of  all  animals 
in  proportion  to  their  weight.  Air-vessels  also  enable 
them  to  blow  out  the  hollow  parts  of  their  bodies, 
when  they  wish  to  make  their  descent  slower,  rise 
more  swiftly,  or  float  in  the  air.  The  muscles  that 
move  the  wings  of  birds  downwards,  in  many  instan- 
ces, are  a  sixth  part  of  the  weight  of  the  whole  body ; 
whereas  those  of  a  man  are  not,  in  proportion,  one- 
hundredth  part  so  large. 

It  is  an  erroneous  idea,  still  taught  in  many  educational  works,  that 
the  bones  of  birds  are  hollow  and  filled  with  air.  This  is  not  the  case. 
Recent  investigations  have  shown  that  the  bones  of  birds,  as  a  general 
thing,  are  not  more  hollow  than  those  of  other  animals,  and  do  not  con- 
tain air. 

150  Why  does  flying  differ  from  leaping  1 

Because  flying  is  the  continued  suspension  and  pro- 
gress of  the  whole  body  in  the  air,  by  the  action  of  the 
wings.  In  leaping,  the  body  is  equally  suspended  in 


SCIENCE   OF  COMMON  THINGS.  27 

Action  of  birds  in  flying.  Action  and  reaction. 

the  air;  but  the  suspension  is  only  momentary.  In 
flying3  on  the  contrary,  the  body  remains  in  the  air 
and  acquires  a  progressive  motion  by  repeated  strokes 
of  the  wings  on  the  surrounding  fluid. 

151  Why  do  birds  stretch  out  their  necks  when  flying  f 

In  order  that  they  may  act  as  a  wedge,  dividing  the 
air  and  diminishing  the  resistance. 

152  Why  are  the  strongest  feathers  of  birds  in  the  pinions  and  tail  f 

Because  when  the  wing  is  expanded,  the  pinion- 
feathers  may  form,  as  it  were,  broad  fans,  by  which 
the  bird  is  enabled  to  raise  itself  in  the  air  and  fly; 
while  its  tail-feathers  direct  its  course. 

153  Why  can  a  person  safely  skate  with  great  rapidity  over  ice  which 
would  not  support  his  weight  if  he  moved  over  it  more  slowly  f 

From  the  fact  that  time  is  required  for  producing 
the  fracture  of  the  ice :  as  soon  as  the  weight  of  the 
skater  begins  to  act  on  any  point,  the  ice,  supported  by 
the  water,  bends  slowly  under  him  ;  but  if  the  skater's 
Velocity  is  great,  he  has  passed  off  from  the  spot  which 
was  loaded  before  the  bending  has  reached  the  point 
which  would  cause  the  ice  to  break. 

154  It  sometimes  happens  when  persons  are  knocked  down  "by  carriages 
that  the  wheels  pass  over  them  with  scarcely  any  injury,  though  if  the  weight 
of  the  carriage  had  rested  on  the  body,  even  for  a  few  seconds,  it  would  have 
crushed  them  to  death.     What  explanation  can  be  given  of  this  fact  f 

The  wheel  moves  with  such  rapidity,  that  the  weight 
has  not  time  sufficient  to  exert  its  full  effect. 

155  When  two  equal  bodies  meet,  moving  with  equal  velocities  in  oppo- 
site  directions,  what  will  be  the  effect  ? 

They  will  both  come  to  rest — for  their  motion  being 
equal  and  contrary,  will  be  mutually  destroyed. 

150  When  two  persons  strike  their  heads  together,  one  being  in  motion 
and  the  other  at  rest,  why  are  both  equally  hurt  f 

Because,  when  bodies  strike  each  other,  action  and 
reaction  are  equal ;  the  head  that  is  at  rest  returns  the 
blow  with  equal  force  to  the  head  that  strikes. 

157  When  an  elastic  batt  is  thrown  against  the  side  of  a  house  with  a 
certain  force,  why  does  it  rebound  f 


28  SCIENCE   OF   COMMON   THINGS. 


Examples  of  action  and  reaction.  Laws  of  falling  bodies. 

Because  the  side  of  the  house  resists  the  ball  with 
the  same  force,  and  the  ball,  being  elastic;  rebounds. 

158  When  the  same  ball  is  thrown  against  a  pane  of  glass  with  the 
same  force,  it  goes  through,  breaking  the  glass :  why  does  it  not  rebound  as 
beforef 

Because  the  glass  has  not  sufficient  power  to  resist 
the  full  force  of  the  ball :  it  destroys  a  part  of  the  force 
of  the  ball,  but  the  remainder  continuing  to  act,  the 
ball  goes  through,  shattering  the  "glass. 

159  Why  did  not  the  man  succeed  who  undertook  to  make  a  fair  wind 
for  his  pleasure  boat,  by  erecting  an  immense  bellows  in  the  stern,  and  blow- 
ing against  the  sails  f 

Because  the  action  of  the  stream  of  wind  and  the 
reaction  of  the  sails  were  exactly  equal,  and,  conse- 
quently, the  boat  remained  at  rest 

160  If  he  had  blown  in  a  contrary  direction  from  the  sails,  instead  of 
against  them,  would  the  boat  have  moved  ? 

It  would,  with  the  same  force  that  the  air  issued  from 
the  bellows-pipe. 

161  Why  cannot  a  man  raise  himself  over  a  fence  by  pulling  upon  the 
straps  of  his  boots  f 

Because  the  action  of  the  force  exerted  to  raise  him- 
self, is  exactly  counteracted  by  the  reaction  of  the  force 
which  tends  to  keep  him  down. 

163  Does  a  man,  in  rowing,  drive  the  water  astern  with  the  same  fores 
that  he  impels  the  boat  forwards  t 

He  does  :  action  and  reaction  being  exactly  equal. 

163  Why  is  it  more  dangerous  to  leap  from  a,  high  window  than  from 
a  low  table  ? 

Because  the  velocity  of  a  falling  ~body,  and,  conse- 
quently, the  force  with  which  it  will  strike  the  ground," 
^ncrease8  with  the  distance  through  which  it  falls. 

164  How  far  ivitt  a,  body  fall,  through  the  influence  of  gravity,  in  one 
te.cond  of  time  ? 

Sixteen  feet. 

165  How  far  will  it  fall  in  two  seconds  f 

Four  times  16  feet,  or  64  feet ;  in  three  seconds  it 
will  fall  144  feet ;  in  four,  256  ;  in  five  seconds,  400 
feet,  and  so  on. 


SCIENCE   OF   COMMON   THINGS.  20 

Pendulum.  Common  clock. 

166  Will  a  mass  of  iron,  weighing  one  hundred  pounds,  let  fall  from 
an  elevation,  reach  the  ground  any  quicker  than  a  mass  weighing  only  one 
pound,  ktfall  at  the  same  time  and  from  the  same  place  f 

No  ;  the  lighter  mass  will  fall  with  the  same  velocity, 
and  reach  the  ground  as  soon  as  the  larger  one. 

Before  the  time  of  Galileo  it  was  taught  and  believed,  that  if  two 
bodies  of  different  weights  were  let  fall  from  any  height  at  the  same  mo- 
ment, the  heavier  body  would  reach  the  ground  as  much  sooner  as  ita 
weight  was  greater  than  the  smaller.  Galileo,  on  the  contrary,  main- 
tained that  they  would  both  strike  the  ground  at  the  same  time,  and,  as 
his  doctrine  was  generally  disbelieved,  he  challenged  his  opponents  to  a 
practical  trial.  The  experiment  was  made  from  the  top  of  the  celebrated 
leaning  tower  of  Pisa,  in  the  presence  of  a  great  concourse  of  people,  and 
resulted  in  the  complete  triumph  of  Galileo. 

167  What  is  the  rule  by  which  the  height  from  which  a  body  falls  may 
be  found,  the  time  consumed  in  falling  being  known? 

Multiply  the  square  of  the  number  of  seconds  of  time 
consumed  in  falling,  ~by  the  distance  which  a  body  will 
fall  in  one  second. 

168  If  a  stone  is  five  seconds  in  falling  from  the  top  of  a  precipice,  hoio 
high  is  the  precipice  f 

The  square  of  five  seconds  is  25  ;  this  multiplied  by 
16,  the  number  of  feet  a  lody  will  fall  in  one  second, 
gives  400,  the  height  of  the  precipice. 

169  What  is  a  pendulum  ? 

A  pendulum  is  a  heavy  body,  as  a  piece  of  metal, 
suspended  by  a  wire  or  cord,  so  as  to  swing  backwards 
and  forwards. 

170  When  is  a  pendulum  said  to  vibrate  f 

When  it  swings  backwards  and  forwards ;  and  that 
part  of  the  circle  through  which  it  vibrates,  is  called 
its  arc. 

17*1   What  is  a  common  clock  f 

Merely  a  pendulum,  with  wheel- work  attached  to  it, 
to  record  the  number  of  vibrations,  and  with  a  weight 
or  spring,  having  force  sufficient  to  counteract  the  re- 
tarding effects  of  friction  and  the  resistance  of  the  air. 

17S  How  long  must  a  pendulum  be  to  beat  seconds  1 

About  39  inches. 

178   Why  does  a  common  clock  go  faster  in  winter  than  in  summer  t 
2* 


30  SCIENCE   OF   COMMON   THINGS. 

Length  of  pendulum  affects  the  rate  of  a  clock. 

Because  the  pendulum-rod  becomes  contracted  by 
cold  in  winter,  and  lengthened  by  heat  in  summer. 

174:  Why  does  a  change  in  the  length  of  the  pendulum  cause  a  clock  to 
go  faster  or  slower  f 

The  number  of  vibrations  which  a  pendulum  makes 
in  a  giyen  time  depends  upon  its  length,  because  a 
long  pendulum  does  not  perform  its  journey  to  and 
from  the  corresponding  points  of  its  arc  so  soon  as  a 
short  one. 


SCIENCE  OF  COMMON  THINGS.  31 

Application  of  power.  What  are  machines  ? 


PART  n. 

APPLICATION   OF   THE   LAWS  AND   PROPER 
TIES  OF  MATTER  TO  THE  ARTS. 


CHAPTER   I. 

HOW  WE  APPLY   POWEB. 

175  What  is  a  machine  f 

By  a  machine  we  understand  a  combination  of  me- 
chanical powers  adapted  to  vary  the  direction,  applica- 
tion, and  intensity  of  a  moving  force,  so  (is  to  produce 
a  given  result. 

176  What  is  the  difference  between  a  machine  and  a  tool  ? 

The  difference  between  a  machine  and  a  tool  is  not 
capable  of  very  precise  distinction.  A  tool  is  usually 
'more  simple  than  a  machine :  it  is  generally  used  by 
hand,  while  a  machine  is  generally  moved  by  some 
vther  than  human  power. 

177  Does  a  machine  ever  create  power,  or  increase  the  quantity  of 
power  or  force  applied  to  it? 

A  machine  will  enable  us  to  concentrate  or  divide 
any  kind  or  quantity  of  force  which  we  may  possess, 
but  it  no  more  increases  the  quantity  of  force  than  a 
mill-pond  increases  the  quantity  of  water  flowing  in 
the  stream. 

178  From  what  sources  do  we  derive  advantages  by  the  use  of  machines 
and  manufactures  f 

From  the  addition  they  make  to  human  power ; 
from  the  economy  they  produce  of  human  time  ;  from 
the  conversion  of  substances  apparently  common  and 
worthless  into  valuable  products. 


32  SCIENCE   OF   COMMON   THINGS. 

Object  of  machinery.  Perpetual  motion.  Sources  of  power. 

179  How  do  machines  make  additions  to  human  power  f 

They  enable  us  to  use  the  powers  of  natural  agents, 
as  wind,  water,  steam;  they  also  enable  us  to  use  ani- 
mal power  with  greater  effect,  as  when  we  move  an 
object  easily  with  a  lever,  which  we  could  not  with  the 
unaided  hand. 

ISO  How  do  machines  produce  economy  of  human  time  f 
They  accomplish  with  rapidity  what  would  require 
the  hand  unaided  much  time  to  perform.     A  machine 
turns  a  gun-stock  in  a  few  minutes ;  to  shape  it  by 
hand  would  be  the  work  of  hours. 

181  How  do  machines  convert  objects  apparently  worthless  into  valuable, 
products  f 

By  their  great  power,  economy,  and  rapidity  of  ac- 
tion, they  make  it  profitable  to  use  objects  for  manu- 
facturing purposes  which  it  would  be  unprofitable  or 
impossible  to  use  if  they  were  to  be  manufactured  by 
hand.  Without  machines,  iron  could  not  be  forged 
into  shafts  for  gigantic  engines ;  fibres  could  not  be 
twisted  into  cables  ;  granite,  in  large  masses,  could  not 
be  transported  from  me  quarries. 

182  Why  are  so  many  attempts  continually  made  to  produce  mechani- 
cal engines  which  shatt  generate  perpetual  motion  f 

Because  the  projectors  do  not  understand  the  great 
truth,  that  no  form  or  combination  of  machinery  can, 
under  any  circumstances,  increase  the  quantity  of  power 
applied. 

183  What  is  the  object  ef  a  machine  f 

To  receive  and  distribute  motion  derived  from  an 
external  agent,  since  no  machine  is  capable  of  generat- 
ing motion  or  moving-power  within  itself. 

184  What  are  the  principal  sources  from  whence  power  is  obtained  f 

Men  and  animals,  water,  wind,  steam,  and  gunpow- 
der. The  power  of  all  these  may  be  ultimately  re- 
solved into  those  of  muscular  energy,  gravity,  heat, 
and  chemical  affinity. 

185  Are  there  any  other  sources  ofpotver  ? 

Yes ;  magnetism,  electricity,  capillary  attraction,  etc. ; 


SCIENCE   OF  COMMON   THINGS  33 

Muscular  energy.  Horse-power.  Water-power. 

but  none  of  these  are  capable  of  being  used  practically 
for  the  production  of  motion. 

186  How  is  muscular  energy  exerted  f 

Through  the  contraction  of  the  fibres  which  constitute 
animal  muscles.  The  bones  act  as  levers  to  facilitate 
and  direct  the  application  of  this  force,  the  muscles 
operating  on  them  through  the  medium  of  tendons,  or 
otherwise. 

187  What  animals  possess  the  greatest  amount  of  muscular  power  f 

Beasts  of  prey.  Some  very  small  creatures,  how- 
ever, possess  muscular  power  in  proportion  to  their 
bulk,  incomparably  greater  than  that  of  the  largest 
and  greatest  of  the  brute  creation.  Kflea,  considered 
relatively  to  its  size,  is  far  stronger  than  an  elephant  or 
a  lion. 

188  In  what  method  can  a  man  exert  the  greatest  active  strength  f 

In  pulling  upwards  from  his  feet :  because  the 
strong  muscles  of  the  back,  as  well  as  those  of  the  up- 
per and  lower  extremities,  are  then  brought  advan- 
tageously into  action.  Hence  the  action  of  rowing  is 
one  of  the  most  advantageous  modes  of  muscular  action. 

189  What  is'the  estimate  of  the  uniform  strength  of  an  ordinary  man 
for  the  performance  of  daily  mechanical  labor  ? 

That  he  can  raise  a  weight  of  10  pounds  to  the  height 
of  10  feet  once  in  a  second,  and  continue  to  labor  for 
10  hours  in  the  day. 

10O  What  is  a  "  horse-power  ?"  We  say  a  steam-engine  is  of  a  cer- 
tain horse-power ;  what  is  the  meaning  of  the  term  ? 

The  measure  of  a"  horse's  power"  adopted  as  a 
standard  for  estimating  the  power  of  steam-engines,  is 
that  he  can  raise  a  weight  of  33,000  pounds  to  the 
height  of  one  foot  in  a  minute. 

191   What  is  the  strength  of  a  horse  compared  with  that  of  man  f 

The  force  of  one  horse  is  considered  to  be  equal  to 
that  of  five  men. 

193    What  do  we  mean  by  "  water-power  f" 

The  power  obtained  by  the  action  of  water, — applied 
generally  to  the  circumference  of  wheels,  which  it 


34:  SCIENCE   OF   COMMON   THINGS. 

Water- wheels.  Power  of  steam.  Gunpowder. 

causes  to  revolve,  either  by  its  weight^  by  its  lateral 
impulse,  or  "by  both  conjointly. 


Fig.  8.  Fig  9. 


The  most  common  forms  of  water-wheels  in  use  are  the  under-shot  and 
over-shot,  or  breast-wheels.  In  the  under-shot  wheel,  Fig  8,  a  stream  of 
water  strikes  against  the  "  float-boards  "  or  paddles,  placed  so  as  to  receive 
the  impulse  of  the  water  at  right  angles  to  the  radii  or  spokes  of  the 
wheel.  In  over-shot  or  breast- wheels,  Fig.  9,  the  water  is  received  in 
cells  or  buckets  on  the  top  or  side.  In  this  case  the  wheel  revolves 
through  the  agency  of  the  weight  of  the  water. 

103  Upon  what  does  the  power  of  steam  depend  t 

Upon  the  tendency  which  water  possesses  to  expand 
into  vapor  when  heated  to  a  certain  temperature. 

194   What  is  gunpowder  f 

A  solid  explosive  substance,  composed  of  saltpetre  or 
nitre,  sulphur,  and  charcoal,  reduced  to  powder,  and 
mixed  intimately  with  each  other. 

105  Upon  what  does  the  power  of  gunpowder  depend  f 

When  brought  in  contact  with  any  ignited  substance, 
it  explodes  with  great  violence.  A  vast  quantity  of 
gas,  or  elastic  fluid,  is  emitted,  the  sudden  production 
of  which,  at  a  high  temperature,  is  the  cause  of  the 
violent  effects  which  this  substance  produces. 

106  Is  the  power  produced  in  the  explosion  of  powder  ever  used  for 
propelling  machinery  regularly  f 

It  is  not,  on  account  of  its  expensiveness  and  the  sud- 
denness and  violence  of  its  action.  It  is  chiefly  applied 
to  the  throwing  of  shot  and  other  projectiles,  and  the 
blasting  of  rocks. 

107'  What  is  (he  estimated  force  of  gunpowder  when  exploded  t 


SCIENCE   OF   COMMON   THINGS.  35 

Properties  of  a  gun.  Range  of  cannon.  Explosive  substances. 

At  least  14,750  pounds  upon  every  square  inch  of 
the  surface  which  confines  it. 

198  What  are  the  essential  properties  of  a  gun  ? 

To  confine  the  elastic  fluid  generated  by  the  explo- 
sion of  the  powder  as  completely  as  possible,  and  to 
direct  the  course  of  the  ball  in  a  straight  or  rectilinear 
path. 

199  Why  will  a  rifle  send  a  ball  more  accurately  than  a  musket,  or 
ordinary  gun  ? 

The  space  produced  by  the  difference  of  diameter 
between  the  tall  and  the  bore  of  the  gun  greatly  di- 
minishes the  effect  of  the  powder,  by  allowing  a  part 
of  the  elastic  fluid  to  escape  before  the  ball,  and  also 
permits  the  ball  to  deviate  from  a  straight  line.  The 
advantage  of  the  rifle-barrel  is  chiefly  derived  from 
the  more  accurate  contact  of  the  ball  with  the  sides  of 
its  cavity. 

J3OO  To  what  distance  may  a  ball  be  thrown  by  a  twenty-four  pounder  f 

"With  a  quantity  of  powder  equal  to  two-thirds  the 
weight  of  the  ball,  it  may  be  thrown  about  four  miles. 

The  effective  range  of  a  twenty-four  pounder  is,  however  much  less 
than  this. 

SOI  How  much  further  would  the  same  ball  go,  were  the  resistance  of 
the  air  removed  ? 

About  five  times  the  distance,  or  twenty  miles. 

2OS   Why  is  gunpowder  always  manufactured  in  little  grains  f 

In  order  to  cause  it  to  explode  more  quickly,  by  faci' 
litating  the  passage  of  the  flame  among  the  particles.* 

2O3  By  what  terms  are  cannon  of  different  sizes  distinguished '? 

By  the  weight  of  the  hall  which  they  are  capable  of 
discharging.  Thus,  we  have  68-pounders,  24-pounders, 
18-pounders,  and  the  lighter  field-pieces,  from  4  to 
12-pounders. 

J3O4  Are  there  any  more  explosive  substances  than  gunpowder  f 

Yery  many ;  but  all  of  them  are  too  expensive  or 
dangerous  for  practical  use. 

SO5  By  whom  was  gunpowder  supposed  to  have  been  discovered  f 

It  is  generally  agreed  that  gunpowder  was  used  by 


36  SCIENCE   OF   COMMON  THINGS. 


Strength  of  materials.  Hollow  tubes. 


the  Chinese  many  centuries,  before  the  Christian  era. 
In  Europe,  its  composition  and  properties  were  dis- 
covered by  Berthold  Schwartz,  a  Prussian  monk,  ins 
the  twelfth  century.  It  was  first  used  in  battle  inl 
1346. 


CHAPTEE    II. 

STRENGTH   OF   MATERIALS. 

SOQ  When  materials  are  employed  for  mechanical  purposes,  upon  what 
does  their  power  or  strength,  apart  from  the  nature  of  ti*e  material,  depend 
for  resisting  external  force? 

Upon  the  shape  of  the  material,  its  hearing,  and  the 
nature  of  the  force  applied  to  it. 

SO7  In  what  position  witt  a  bar  or  learn  sustain  the  greatest  application 
of  force  f 

When  it  is  strained  in  the  direction  of  its  length. 

SOS   What  do  we  mean  by  stiffness  of  a  material  f 

It  is  the  resistance  to  the  application  of  force  tending 
to  bend  it. 

509  How  much  stiffer  is  a  beam  supported  at  both  ends,  than  one  of 
hall  the  length  firmly  faced  at  only  one  end? 

Twice  as  stiff. 

510  In  what  form  can  a  given  quantity  of  matter  be  arranged  so  as  to 
oppose  the  greatest  resistance  to  a  bending  force  f 

In  the  form  of  a  hollow  tube  or  cylinder. 

511  Why  are  the  bones  of  man  and  animals  hollow  and  cylindrical  f 

Because  in  this  form  they  can  with  the  least  weight 
of  material  sustain  the  greatest  force.  In  man  and 
animals,  the  hollow  part  of  the  bones  is  filled  with  an 
oily  substance  called  marrow. 

SIS   Why  are  the  quills  of  birds  hottow  and  empty  of  marrow  t 


SCIENCE   OF   COMMON   THINGS.  37 


Stems  of  grasses  hollow.  Limit  to  the  size  of  ships. 


In  order  that  they  may  possess  the  greatest  strength, 
and  by  their  lightness  assist  in  flying. 

213    Why  are  the  stems  of  seeds  and  grain-bearing  plants  hollow  tube?  1 

Because  this  disposition  of  matter  gives  to  the  stalk 
its  greatest  strength,  enables  it  to  resist  the  action  of 
*the  wind,  and  sustain,  without  breaking,  the  ripened 
ear  of  grain  or  seed. 

314  Is  a  column  with  ridges  projecting  from  it,  stronger  than  one  that 
w  perfectly  smooth  f 

It  is. 

SIS  Why  is  a  hoUow  tube  of  metal  stronger  than  tfie  same  quantity  of 
metal  as  a  solid  rod  f 

.  Because  its  substance  standing  farther  from  the 
centre,  has  a  greater  power  of  resisting  a  bending 
force. 

S1G  Of  two  bodies  of  similar  shape,  but  of  different  sizes,  which  is  pro- 
portionably  the  weaker  f 

The  larger.  That  a  large  body  may  have  propor- 
tionate strength  to  a  smaller,  it  must  have  a  greater 
proportionate  amount  of  material ;  and  beyond  a  cer- 
tain limit,  no  proportions  whatever  will  keep  it  to- 
gether ;  but  it  will  fall  in  pieces  by  its  own  weight. 

SIT*    Why  cannot  trees  attain  an  unlimited  height  of  trunk  f 

Because,  beyond  a  certain  limit,  the  weight  of  the 
material  will  overcome  the  supporting  strength  of  the 
material. 

£18   Why  is  it  impracticable  to  build  ships  beyond  a  certain  size  f 

Because  the  weight  of  the  timber  and  other  materials 
contained  in  them  tends  to  cause  them  to  fall  apart. 

In  1825,  two  vessels,  the  largest  ever  constructed,  were  built  in  Ca- 
nada, of  10,000  tons  burden.  They  were  found  to  be  weak  from  their 
size  alone,  and  were  both  lost  on  their  first  voyage. 


SCIENCE   OF  COMMON  THINGS. 


Ce»enta.  Quicklime.  Whitewash. 


CHAPTEE   III. 

APPLICATION   OF   MATERIALS   FOB   ARCHITECTURAL  OR 
STRUCTURAL   PURPOSES. 

210   What  are  cements? 

Cements  are  for  the  most  part  soft  or  semi-fluid  sub- 
stances which  have  the  property  of  becoming  hard  in 
time,  and  cohering  with  other  bodies  to  which  they  have 
been  applied. 

22O  Of  what  are  the  ordinary  cements  which  are  called  mortars  com- 
posed f 

Of  quicklime,  sand,  and  water. 

{321   What  is  quicklime? 

Quicklime  is  principally  pure  lime,  and  is  obtained, 
from  the  limestone  rock,  ordinary  marble,  or  shellr, 
which  are  composed  of  carbonate  of  lime,  by  calcina 
tion.     The  effect  of  the  burning  is  to  drive  on  the  car- 
bonic acid,  leaving  the  lime  pure  and  uncombined. 

J3SS   What  is  slacked  lime  f 

If  quicklime  obtained  as  above  described  be  wet 
with  water,  it  instantly  swells  and  cracks,  becomes 
exceedingly  hot,  and  at  length  falls  into  a  white,  soft, 
impalpable  powder.  This  is  denominated  "slacked 
lime. 

223  What  is  ordinary  whitewash  f 

A  mixture  of  slacked  lime  with  water. 

224  Why  should  slacked  lime  intended  for  mortars  be  excluded  from 
the  air,  or  used  soon  after  it  has  been  prepared  f 

Because  if  exposed  to  the  air  it  absorbs  carbonic 
acid,  and  becomes  converted  again  into  its  former  con- 
dition of  carbonate  of  lime. 

225  Why  does  mortar  become  hard  after  a  few  days  f 

A  portion  of  the  water  evaporates,  and  the  lime  by 
a  sort  of  crystallization  adheres  to  the  particles  of  sand 


SCIENCE   OF  COMMON  THINGS.  39 

Mortar.  Htucco.  Color  of  bricks. 

and  unites  them  together.     The  lime  also  gradually 
becomes  converted  into  carbonate  of  lime. 

336    What  sand  is  mest  suitable  for  the  formation  of  mortar  f 

That  which  is  wholly  silicious  and  is  sharp  /  that  is, 
not  having  its  particles  rounded  by  attrition. 

337*   What  are  the  proportions  of  lime  and  sand  in  good  mortar  f 

The  proportions  are  varied  in  different  places :  the 
amount  of  sand,  however,  always  exceeds  that  of  the 
lime.  The  more  sand  that  can  be  incorporated  with 
the  lime  the  better,  provided  the  necessary  degree  of 
plasticity  is  preserved. 

338   What  are  water,  hydraulic,  or  Roman  cements  f 

Those  which  have  the  property  of  hardening  under 
water,  and  of  consolidating  almost  immediately  on  be- 
ing mixed. 

330  To  what  cause  do  the  water-cements  owe  their  property  of  becoming 
hard  under  water  f 

The  cause  is  not  satisfactorily  known :  all  water- 
cements  contain  a  portion  of  burnt  clay,  which  proba- 
bly absorbs  immediately  all  superabundant  moisture 
from  the  lime,  and  thus  expedites  its  solidification. 

This  explanation  is  rendered  more  probable  from  the  fact,  that  if  the 
clay  is  burnt  sufficient  to  vitrify  it  or  convert  it  into  brick,  it  ceases  to 
form  a  water-cement. 

330  What  are  the  constituents  of  a  water-cement  f 

Quicklime,  sand  or  silica,  and  a  proportion  of  clay. 

331  What  is  stucco  f 

Stucco  is  composed  of  various  ingredients,  generally 
of  "plaster  of  Paris,"  sometimes  ot  white  marble  pul- 
verized and  mixed  with  plaster  and  lime. 

333   What  is  terra-cotta  f 

Literally,  baked  clay,  a  name  given  to  statues,  archi- 
tectural ornaments,  vases,  figures,  etc.,  modelled  of 
potters'-clay  and  fine  colorless  sand,  and  afterwards 
exposed  to  a  most  intense  heat. 

333   Why  are  bricks  when  burned  usually  of  a  red  color  ? 

Because  the  iron  contained  in  the  clay  is  converted 


4:0  SCIENCE   OF   COMMON   THINGS. 

Brides  with  straw.  Tiles]  Mastic. 

by  the  heat  into  the  red  oxide  of  iron,  and  acts  in  this 
state  as  red  coloring  material. 

334  Why  are  the  bricks  manufactured  at  Chicago,  and  some  other 
parts  of  the  Western  country,  of  a  white  or  yettow  color  f 

Because  the  clay  of  which  they  are  formed  does  not 
contain  sufficient  iron  to  color  them. 

335  Why  did  the  children  of  Israel  in  making  bricks  desire  to  mix 
straw  with  the  clay  f 

j,  The  bricks  of  the  Egyptians  were  composed  of  clay 
simply  baked  in  the  sun,  and  not  burnt.  By  using 
straw  the  clay  was  held  together  more  firmly  and  the 
brick  rendered  stronger. 

336  Why  are  the  Egyptians  enabled  to  dispense  with  the  process  of 
burning  the  bricks  ? 

The  extreme  dryness  of  the  climate  in  which  they 
were  used  enable  them  to  dispense  with  the  burning. 
Bricks  from  Egypt  and  Babylon,  which  have  remained 
exposed  to  the  open  air  uninjured  for  two  thousand 
years,  rapidly  fall  to  pieces  when  transported  to  a 
moist  climate. 

237   Why  do  we  mix  hair  with  mortar  f 

In  order  to  render  it  more  cohesive  and  stronger. 

338  What  are  tiles  f 

Plates  of  burnt  clay  resembling  bricks  in  composi- 
tion and  manufacture,  and  used  for  the  coverings  of 
roofs  or  floors. 

339  What  is  mastich  or  mastic  t 

The  name  given  to  those  cements  which  contain  ani- 
mal or  vegetable  substances  in  composition.  Mastich 
used  for  the  external  decoration  of  houses  often  con- 
tains oil  and  a  preparation  of  lead. 

340  What  is  putty? 

Putty,  used  by  glaziers  in  setting  window-glass  and 
for  other  purposes,  is  composed  of  whiting  and  linseed- 
oil,  mixed  and  worked  together.  "Whiting  is  simply 
common  chalk  ground  and  purified. 


SCIENCE   OF   COMMON   THINGS. 


Principles  of  architecture.  Properties  of  a  good  building. 


CHAPTER 

PRINCIPLES    OF   ARCHITECTURE 
341   What  is  architecture  ? 

In  its  general  sense  it  is  the  art  of  erecting  buildings. 
In  modern  use,  this  name  is  often  restricted  to  the  ex- 
ternal forms  or  styles  of  building. 

343  To  what  cause  do  the  different  varieties  of  architecture  owe  their 
origin  ? 

To  the  rude  structures  which  the  climate  or  materials 
of  any  country  obliged  its  early  inhabitants  to  adopt 
for  temporary  shelter. 

These  structures  with  all  their  prominent  features  have  been  afterwards 
kept  up  by  their  refined  and  opulent  posterity.  Thus  the  Egyptian  style 
of  architecture  had  its  origin  in  the  cavern  or  mound;  the  Chinese  archi- 
tecture is  modelled  from  the  tent;  the  Grecian  is  modelled  from  the 
wooden  cabin ;  and  the  Gothic  from  the  boiver  of  trees. 

343  What  kind  of  shape  is  it  most  probable  that  the  fa'st  human  habi- 
tations assumed  ? 

We  have  every  reason  to  believe  that  huts  of  a 
conical  form  were  first  constructed. 

344  Why? 

First,  on  account  of  their  being  easily  erected,  and 
as  easily^  removed ;  secondly,  because  their  declivity 
on  all  sides  would  cause  the  rain  to  run  off;  and, 
thirdly,  owing  to  their  breadth  at  the  base  and  their 
gradually  growing  to  a  point  at  the  top,  they  were 
capable  of  resisting  the  ordinary  force  of  the  wind. 

345  Are  conical  huts  anywhere  in  use  at  the  present  time  f 

Yes  ;  we  find  them  still  used  by  the  uncultivated  in- 
habitants of  the  South  Sea  Islands,  by  the  American 
Indians,  by  the  Hottentots,  the  Kamskatschans,  and 
other  uncivilized  tribes. 

346  What  are  the  three  chief  properties  of  a  good  building  f 

Usefulness,  strength,  and  beauty. 

347*  Ifrw  are  they  to  be  attained  f 


SCIENCE  OF  COMMON   THINGS. 


Essentials  for  building.  Pile. 


Mortising. 


The  proper  arrangement  of  the  respective  parts  of 
the  building  will  insure  its  usefulness.  Its  strength 
will  principally  depend  on  the  walls  being  laid  on  a 
good  and  firm  foundation,  of  sufficient  thickness  at  the 
bottom,  and  standing  perfectly  perpendicular.  And  if 
all  the  parts  of  a  building  correspond  with  each  other, 
and  are  handsome  in  themselves,  then  the  architect 
may  rely  on  its  beauty. 

S4S   What  are  the  essential  elementary  parts  of  a  "building  f 

Those  which  contribute  to  its  support,  indosure,  and 
covering. 

J349   What  is  a  pile? 

A  cylinder  of  wood  or  metal  pointed  at  one  extremity 
and  driven  forcibly  into  the  earth,  to  serve  as  a  support 
or  foundation  of  some  structure.  It  is  generally  used 
in  marshy  or  wet  places,  where  a  stable  foundation 
could  not  otherwise  be  obtained. 

25O  Why  are  long  columns  supporting  great  weights  made  smaller- at 
the  top  than  at  the  bottom  f 

Because  the  lower  part  of  the  column  must  sustain, 
not  only  the  weight  of  the  superior  party  but  also  the 
weight  which  presses  equally  on  the '  whole  column. 
Therefore  the  thickness  of  the  column  should  gradually 
decrease  from  bottom  to  top. 

251  In  the  construc- 
tion of  buildings  various 
terms  are  employed  to  de- 
signate the  method  in 
which  the  timbers  are 
fitted  into  each  other:  what 
do  we  mean  by  mortising  ? 

Mortising  is  a 
method  of  insertion 
in  which  the  pro- 
jecting extremity 
of  one  timber  is 
received  into  a  perforation  in  another.  (See  Jig.  10.) 

S32  Why  are  steep  roofs,  or  those  constructed  with  considerable  incli- 
nation, best  adapted  for  houses  in  cold  climates  ? 

In  order  that  the  snow  may  not  be  retained  upon 


Fig.  10. 


SCIENCE   OF   COMMON   THINGS. 


43 


Tenons.  Scarfing.  Tongueing.  Arch. 

them,  which  otherwise  would  be  liable  to  injure  the 
building  by  its  weight. 

253  What  is  a  mortise  ? 

The  opening  or  hole  cut  in  one  piece  of  wood  to 
admit  the  projecting  extremity  of  another  piece. 

254  What  is  a  tenon? 

The  end  of  a  piece  of  timber  which  is  reduced  in  di- 
mensions so  as  to  be  fitted  into  a  mortise  for  fastening 
two  timbers  together. 

255  What  is  scarfing  and  interlocking  t 

It  is  that  method  of  insertion  in  which  the  ends  of 
pieces  overlay  each  other,  and  are  indented  together,  so 
as  to  resist  longitudinal  strain  by  extension,  as  in  tie 
bearers  and  the  ends  of  hoops.  (See  fig.  11.) 


256  What  is  tongueing  and  rabbeting  f 

It  is  that  method  of  insertion  in  which  the  edges  of 
boards  are  wholly  or  partially  received  by  channels  in, 
each  other. 

257  What  is  an  arch  t 

It  is  a  part  of  a  structure  or  building  suspended  over 
a  hollow,  and  concave  towards  the  area  of  the  hollow. 

253  Is  it  known  at  what  time  the  arch  was  invented  ? 

It  is  not ;  it  does  not  appear  to  have  been  known  to 
the  ancients. 

259  Why  is  an  arch  capable  of  resisting  a  greater  amount  of  pressure 
than  a  horizontal  or  rectangular  structure  constructed  of*  the  same  ma- 
terials f 

Because  the  arrangement  of  the  materials  composing 


44  SCIENCE   OF  COMMON   THINGS. 


Dovetailing.  Construction  of  the  skull.  Egg-shells. 


the  arch  is  such,  that  the  force  which  would  break  a 
horizontal  beam  or  structure  is  made  to  compress  all  the 
^articles  of  the  arch  alike,  and  they  are  therefore  in  no 
danger  of  being  torn  or  overcome  separately. 

S6O   What  is  meant  by  dovetailing? 

It  is  a  method  of  insertion  in 
which  the  parts  are  connected 
~by  wedge-shaped  indentations, 
which  permit  them  to  be  sepa- 
rated only  in  one  direction.  (See 

F«.  12. """        '    J1^'  *rv 

SGI  What  beautiful  application  of  the  arch  exists  in  the  human  struc- 
ture ?  ~ 

In  the  skull,  protecting  the  brain.  The  materials 
are  here  so  arranged  as  to  present  the  greatest  strength, 
with  the  least  weight. 

S6J3  Why  is  it  difficult  to  break  an  egg  by  pressing  directly  upon  its 
ends  ? 

Because  the  shell  of  the  egg  is  constructed  on  the 
principle  of  the  arch,  and  is  therefore  capable  of  re- 
sisting great  pressure. 

SG3  Why  is  a  dished  or  arched  wheel  of  a  carriage  much  stronger  for 
resisting  all  kinds  of  shocks  than  a  flat  wheel? 

In  an  arched  or  dished  wheel,  the  extremity  of  a 
spoke  cannot  be  displaced  inwards,  or  towards  the  car- 
riage, unless  the  rim  of  the  wheel  be  enlarged,  or  all 
the  other  spokes  yield  at  the  same  time ;  and  it  cannot 
be  displaced  outwards,  unless  the  rim  be  diminished, 
or  the  other  spokes  yield  in  an  opposite  direction. 

Now  the  rim,  being  strongly  bound  with  a  tire  of  iron,  cannot  suffer 
either  increase  or  diminution,  and  the  strength  of  all  the  spokee  is  thus 
conferred  by  it  on  each  individually.  In  a  flat  wheel,  a  given  degree  of 
displacement,  outwards  or  inwards,  of  the  extremities  of  a  spoke,  would 
less  affect  the  magnitude  of  the  circumference,  and  therefore  the  rim  of 
such  a  wheel  secures  it  much  less  firmly. 

S64  Why  are  the  fore  wheels  of  carriages  smaller  than  the  hind 
wheels  ? 

Because  they  facilitate  the  turning  of  the  carriage. 
The  advantage  of  the  wheel  is  proportioned  to  the  mag- 


SCIENCE   OF   COMMON   THINGS.  45 


Arch.  Orders  in  architecture,  Gothic  structures. 

nitude ;  the  smaller  wheel  having  to  rise   a   steeper 
curve. 

365  WJiat  is  an  abutment  f 

The  vertical  wall  which  sustains  the  base,  or  "  spring" 
of  an  arch. 

366  What  is  meant  by  an  order  in  architecture  f 

By  an  architectural  order,  we  understand  a  certain 
mode  of  arranging  and  decorating  a  column,  and  the 
adjacent  parts  of  the  structure  which  it  supports  or 
adorns. 

367  How  many  orders  are  recognised? 

five: — the  Doric,  Ionic,  and  Corinthian,  derived 
from  the  Greeks;  to  these  the  Romans  added  two 
others,  known  as  the  Tuscan  and  Composite. 

368  How  do  pilasters  differ  from  columns  f 

Only  in  their  plan,  which  is  square,  as  that  of 
columns  is  round :  pilasters  are  attached  to  walls. 

369  What  is  a  portico  f 

A  portico  is  a  continued  range  of  columns  covered  at 
the  top  to  shelter  from  the  weather.  The  portico  of  the 
temple  at  Palmyra  was  full  four  thousand  feet  long. 

370  What  are  balusters? 

Small  columns,  or  pillars  of  wood,  stone,  <&c.,  used 
in  terraces  or  tops  of  buildings  for  ornament ;  also  to 
support  railing.  When  continued  for  some  distance, 
they  form  a  balustrade. 

371  WJieredidthe  Gothic  order  of  architecture  originate? 

Among  the  northern  nations  of  Europe.  After  the 
destruction  of  the  Roman  empire,  it  was  introduced  to 
the  exclusion  of  the  Greek  and  Roman  manner  of 
architecture.  It  seems  particularly  adapted  to  reli- 
gious edifices. 

373   What  are  the  characteristics  of  the  Gothic  architecture  f 

Pointed  arches,  with  greater  height  than  breadth  in 
the  proportions,  with  profuse  ornament,  chiefly  de- 
rived from  an  imitation  of  the  leaves  and  flowerg  of 
plants. 


4:6  SCIENCE  OF  COMMON  THINGS. 

Bad  taste  in  architecture.  Columns.  Capitals. 

— — — — : .  ..  . '  — —       —     .      — .     * 

373  What  is  said  to  have  been  the  model  of  the  aisle  of  a  Gothic  cathe- 
dral? 

A  group  of  tall  trees,  meeting  at  tlie  top  with,  inter- 
woven branches. 

374  Ought  architecture  to  be  considered  as  a  fine  or  a  useful  art  f 

As  a  useful  art. 

It  is  degrading  the  fine  arts  to  make  them  entirely  subservient  to 
utility.  It  is  out  of  taste  to  make  a  statue  of  Apollo  hold  a  candle,  or  a 
line  painting  stand  as  a  fireboard.  Our  houses  are  for  use,  and  architec- 
ture is  therefore  one  of  the  useful  arts.  In  building,  we  should  plan  the 
inside  first,  and  then  the  outside  to  cover  it. 

375  Why  is  it  bad  taste  to  construct  a  dwelling-house  in  the  form  of  a 
Grecian  temple  f 

Because  a  Grecian  temple  was  intended  for  external 
worship,  not  as  a  habitation  or  a  place  of  meeting. 

370  Had  the  Goths,  who  plundered  Rome,  anything  to  do  with  the 
invention  of  Gothic  architecture  f 

No;  the  name  was  introduced  abont  two  hundred 
years  ago  as  a  term  of  reproach,  to  stigmatize  the 
edifices  of  the  Middle  Ages,  which  departed  from  the 
purity  of  the  antique  models. 

377   What  is  the  facade  of  a  building  t 

Its  front. 

278   What  is  a  pedestal  f 

The  lower  part  or  base  of  the  column ;  a  continued 
base,  on  which  a  range  of  columns  is  erected,  is  called 
a  stylobate. 

379  What  is  the  base  of  a  column  f 

The  lower  part,  where  it  is  distinct  from  the  shaft. 

380  What  is  the  shaft  f 

The  middle  or  longest  part  of  the  column. 

381  What  is  the  capital  f 

The  upper  or  ornamental  part  resting  on  the  shaft. 
The  height  of  a  column  is  measured  in  diameters  of 
the  column  itself,  always  taken  at  the  base. 

383   What  is  the  plinth  f 

This  term  is  applied  to  the  lower  part  of  the  pedestal, 
or  to  any  square  projecting  basis,  such  as  those  at  the 


SCIENCE   OF   COMMON   THINGS. 
Entablaturel  Architrave.  Frieze. 


bottom  of  walls,  and  under  the  base  of  columns.  The 
lower  part  of  the  pedestal  being  called  the  plinth,  the 
middle  part  will  be  termed  the  die,  and  the  upper 
part  the  cornice  of  the  pedestal.  (See  fig.  13.) 


r  Entablature 


Column.. 


Stylobate  or  Pe- 
destal..      ... 


....Plinth. 


283   What  is  the  entablature  f 

The  horizontal  continuous  portion  which  rests  upon 
the  top  of  a  row  of  columns. 

S84   What  is  the  architrave  f 

The  lower  part  of  the  entablature. 

What  is  the  frieze  t 


4:8  SCIENCE   OF   COMMON   THINGS. 

Durability  of  building  materials.  Effect  of  the  atmosphere  on  rocks. 

The  middle  part  of  the  entablature. 

S86   What  is  the  cornice  f 

The  upper  or  projecting  part  of  the  entablature^ 
(For  illustration  of  these  different  terms,  see  fig.  13.) 

28*7  In  selecting  a  stone  for  architectural  purposes,  how  may  we  be  able 
to  form  an  opinion  respecting  its  durability  and  permanence? 

By  visiting  the  locality  from  whence  it  was  obtained, 
we  may  judge  from  the  surfaces  which  have  been  long 
exposed  to  me  weather  if  the  rock  is  liable  to  yield  to 
atmospheric  influences,  and  the  conditions  under  which 
it  does  so. 

"  For  example,  if  the  rock  be  a  granite,  and  it  be  very  uneven  and 
rough,  it  may  be  inferred  that  it  is  not  very  durable;  that  the  feldspar, 
which  forms  one  of  its  component  parts,  is  more  readily  decomposed  by 
the  action  of  moisture  and  frost  than  the  quartz,  which  is  another  ingre- 
dient ;  and  therefore  that  it  is  very  unsuitable  for  building  purposes. 
Moreover,  if  it  possesses  an  iron-brown  or  rusty  appearance,  it  may  be 
set  down  as  highly  perishable,  owing  to  the  attraction  which  this  metal 
has  for  oxygen,  causing  the  rock  to  increase  hi  bulk,  and  so  disintegrate." 

388  Why  are  the  sandstones,  termed  freestones,  ill  adapted  for  the 
external  portions  of  exposed  buildings  f 

Because  they  readily  absorb  moisture  ;  and  in  coun- 
tries where  frosts  occur,  the  freezing  of  the  water  in 
the  wet  surface  continually  peels  off  the  external  por- 
tions, and  thus,  in  time,  all  ornamental  work  upon  the 
stone  will  be  defaced  or  destroyed. 

389  Why  do  some  species  of  rock  become  harder  when  taken  from  the 
quarry  and  exposed  to  the  atmosphere  f 

This  quality,  in  some  species  of  stone,  arises  from 
the  fact  that  the  water  contained  in  it,  when  forming 
part  of  the  natural  rock,  evaporates,  and  the  stone, 
becoming  dryer,  becomes  harder. 

390  Why  do  some  stones,  altlwugh  hard  when  first  quarried,  become 
friable,  and  fall  to  pieces,  when  exposed  to  the  atmosphere '( 

Because  they  contain  clay  or  alumina  in  such  a  state 
as  to  readily  absorb  moisture  from  the  atmosphere ;  and 
through  the  agency  of  the  moisture  the  particles  lose 
their  cohesion  and  tall  apart. 


SCIENCE   OF   COMMON   THINGS.  49 

Laws  and  phenomena  of  fluids.  Water  in  motion  and  at  rest. 

PAET  III. 

THE  LAWS  AND  PHENOMENA  OF  FLUIDS, 


S91  Into  what  two  classes  may  all  fluid  substances  "be  divided? 

Into  liquids,  as  water,  oil,  molasses,  etc. ;  and  into 
gases,  as  common  air,  carbonic  acid  gas,  oxygen,  and 
others. 

J393  What  designation  do  we  give  to  those  branches  of  science,  which 
treat  of  the  laws  and  phenomena  of  liquids  ? 

Hydrostatics,  which  considers  the  laws  and  pheno- 
mena of  water  and  other  liquids  in  a  state  of  rest ;  and 
hydraulics,  which  considers  the  laws  and  phenomena 
of  liquids  in  motion. 

S93  What  designation  do  we  give  to  that  department  of  science  which 
treats  of  the  laws  and  phenomena  of  gases,  and  other  substances  resembling 
air  ? 

We  apply  the  term  Pneumatics  to  that  department 
of  science  which  explains  and  illustrates  those  pheno- 
mena which  arise  from  the  weight,  pressure,  or  motion 
of  common  air  and  other  gaseous  bodies. 


CHAPTEE   I. 

WATER   IN   MOTION   AND   AT   REST. 

S94   When  water  or  any  other  fluid  is  at  rest,  in  what  condition  is  its 
surface  ? 

The  surface  of  water  at  rest  is  always  perfectly  level. 


50 


SCIENCE   OF  COMMON  THINGS. 


Velocity  of  rivers. 


How  we  make  an  aqueduct. 


595  Why  is  the  surface  of  a  fluid  at  rest  always  kvel  ? 

Because  the  particles  are  equally  attracted  towards 
the  earth  ly  gravity,  and  are  all  equally  and  perfectly 
movable  among  themselves. 

596  How  slight  a  declivity  is  sufficient  to  give  a  running  motion  to 
water  ? 

Three  inches  to  a  mile  in  a  smooth,  straight  channel, 
gives  a  velocity  of  about  three  miles  per  hour.  The 
river  Ganges,  at  a  distance  of  1800  miles  from  its 
mouth,  is  only  800  feet  above  the  level  of  the  sea. 

£97  On  what  principle  are  we  enabkd  to  conduct  water  under  ground 
through  irregular  tubes  ? 

On  the  principle  that  water  will  always  rise  to  an 
exact  level  in  different  tubes,  pipes,  or  vessels  communi- 
cating with  each  other. 

If  we  connect  together  a 
series  of  vessels,  no  matter 
how  various  their  shapes  and 
capacities,  so  that  water  may 
rise  from  the  main  channel, 
A  B,  into  them,  we  shall  find 
upon  pouring  water  into  one 
that  it  will  rise  to  the  same 
Fig- 14.  level  in  all  the  vessels. 

The  dependence  of  all  arrangements  for  conveying  water  in  aqueducts 
under  ground  upon  the  principle,  that  water  in  closed  tubes  or  vessels 
rises  to  a  uniform  level,  is  clearly  shown  in  Fig.  15 :  a,  a,  a,  represents 
the  water-level  of  a  pond  or  reservoir  upon  elevated  ground.  From  this 
pond  a  line  of  pipe  is  laid,  passing  over  a  bridge  or  viaduct  at  d,  and 


Fig.  15. 


under  a  river  at  c.     The  fountains,  at  &,  6,  show  the  stream  rising  to  it3 
level  in  the  pond,  a,  at  two  points  of  very  different  elevation. 

S98  In  what  part  of  a  river  does  the  water  flow  most  rapidly  f 

In  the  middle  of  the  stream,  at  the  surface.     On  the 


SCIENCE   OF  COMMON   THINGS.  51 

Origin  of  springs.  How  water  collects  in  wells. 

sides  and  bottom  the  velocity  is  diminished  by  the 
friction  of  the  water  against  the  banks,  bars,  etc. 

S99   Wliat  is  the  origin  of  springs  1 

The  water  falling  upon  the  earth  sinks  downwards 
through  the  sand  and  porous  materials,  until  an  imper- 
vious bed  of  clay  or  rock  is  reached.  Here  the  water 
accumulates,  and  finally  bursts  out  at  some  point  where 
the  impervious  bed  or  strata  comes  to  the  surface  in 
consequence  of  a  valley  or  excavation. 

Suppose  a  (Fig.  16)  to 
be  a  gravel  hill,  and  b 
a  strata  of  clay  or  rock, 
impervious  to  water. 
The  fluid  percolating 
through  the  gravel 
would  reach  the  imper- 
•~~  "  vious  strata,  along 

which  it  would  run  un- 
til it  found  an  outlet  at  c  at  the  foot  of  the  hill,  where  a  spring  would  be 
formed. 

SOO  Why  does  not  the  water  ooze  out  everywhere  along  the  line  of  June* 
tion  of  the  two  formations — the  gravel  and  the  rock  or  clay — so  as  to  form 
one  continuous  land  soak,  instead  of  a  few  springs  only,  and  these  far  distant 
from  one  another  ? 

For  two  reasons :  first,  on  account  of  rents  and  fis- 
sures in  the  layers  of  rock,  which  act  as  natural  drains  • 
secondly,  the  existence  of  inequalities  in  the  surface 
of  the  impermeable  stratum,  which  lead  the  water,  as 
valleys  do  on  the  external  surface  of  a  country,  into 
certain  low  levels  and  channels. 

3O1   Why  does  the  water  coUect  in  an  ordinary  well  f 

An  ordinary  well  consists  of  an  excavation  continued 
until  a  stratum  or  layer  of  clay  or  rock  is  reached  that 
is  permanently  saturated  with  water.  They  are  not 
commonly  supplied  by  springs,  but  merely  by  the 
draining  of  the , water  which  exists  within  the  circuit 
of  a  few  yards  into  a  cavity. 

SOS   Why  do  wells  and  springs  fail  oftentimes  in  dry  weather  f 

Because  they  are  supplied  by  the  water  fallina  as 
rain,  which  percolates  from  the  surface  of  the  earth. 


52  SCIENCE    OF   COMMON   THINGS. 

Artesian  wells. 
SO3    What  is  an  Artesian  weU? 

Water  is  sometimes  obtained  by  Coring  into  the 
earth  with  a  species  of  auger,  until  a  vein  or  sheet  of 
water  is  found,  which  rises  to  the  surface  through  the 
cylindrical  excavation.  Such  excavations  are  called 
Artesian  wells,  because  the  method  was  first  invented 
and  employed  at  Artois,  in  France. 

/(•;    3O4  How  do  you  account  for  the  water  rising  to  the  surface  in  Arte- 
sian, and  sometimes  in  ordinary  wells  ? 

Strata  which  are  pervious  frequently  alternate  with 
others  which  are  not  so ;  or  may  form  a  basin,  the 
area  of  which  is  partially  filled  with  clay,  through 
which  water  cannot  pass ;  in  such  a  case  it  is  obvious 
that  the  bed  of  sand  beneath  the  clay,  fed  by  the  rain 
which  descends  on  the  uncovered  margin  of  the  basin, 
must  form  a  reservoir  where  the  water  will  gradually 
accumulate  beneath  the  central  layer  of  clay,  through 
which  it  cannot  escape.  If  the  bed  of  clay  be  pene- 
trated by  natural  or  artificial  means,  the  water  must 
necessarily  rise  to  the  surface,  and  may  even  be  thrown 
up  in  a  jet  to  an  altitude  which  will  depend  on  the 
level  of  the  fluid  in  the  subterranean  reservoir. 


Fig.  17. 

Thus,  if  a  sandy  stratum,  a  a  (Fig.  17),  acting  as  a  filter,  occupies  an 
inclined  position  between  two  other  strata  impervious  to  water,  such 
as  clay,  the  water  being  absorbed  by  the  superficial  parts  of  the  strata, 
a»  at  a  a  (which  may  be  of  very  great  extent),  will  penetrate  through  its 
whole  depth,  and,  finding  no  egress  below  on  account  of  the  basin-like 
form  of  the  stratum,  or  from  its  resting  at  the  lower  termination  upon  a 
compact  rock,  will  accumulate.  The  porous  strata,  therefore,  becomes  a 
reservoir  tp  a  greater  or  less  extent,  and  if,  by  boring  through  the  super- 
incumbent mass,  we  form  an  opening  into  the  stratum,  as  at  6,  the  water 


SCIENCE   OF   COMMON   THINGS.  53 

Effect  of  drainage  upon  springs.  Pressure  of  water. 

will  rise  in  it,  and  flow  over  in  a  jet  proportional  to  the  height  of  the 
water  accumulated  in  the  stratum  from  whence  it  flows. 

305  What  general  effect  does  the  cultivation  and  drainage  of  a  country 
have  upon  the  springs  ? 

In  a  well  cultivated  and  improved  country  the 
springs  are  comparatively  few  in  number  and  not  con- 
stant, While  the  face  of  a  country  is  rough,  the  rain- 
water remains  long  among  its  inequalities,  slowly  sink- 
ing into  the  earth  ,to  feed  the  springs,  or  slowly  run- 
ning away  from  bogs  and  marshes  towards  the  rivers  ; 
but  in  a  well  drained,  country  the  water  runs  off  quick- 
ly, often  producing  dangerous  floods. 

SOS  How  is  the  pressure  of  water  exerted? 

Equally  in  all  directions. 

SOT*  Does  ivater,  contained  in  a  vessel,  press  with  as  great  force  against 
t)ie  sides  and  top  as  against  the  bottom  ? 

The  pressure,  in  all  directions,  is  the  same 

SOS  What  is  the  result  if  a  corked  empty  bottle  be  lowered  into  the 
ocean  for  a  considerable  depth  ? 

The  cork  is  generally  forced  inwards  at  a  given 
depth,  no  matter  in  what  direction  the  mouth  of  the 
bottle  may  happen  to  point. 

SOD  Jf  the  cork  is  fastened  immovably  into  the  bottle,  what  will  be  the 
effect? 

The  bottle  will  be  crushed  inwards  by  the  pressure 
before  it  reaches  a  depth  of  sixty  feet. 

S1O  When  a  ship  founders  in  shallow  water,  the  wreck,  on  breaking  to 
pieces,  generally  comes  to  the  surface  and  is  cast  upon  the  shore ;  but  when 
a  ship  sinks  in  very  deep  water,  it  never  rises :  why  is  this  f 

The  pressure  of  very  deep  water  forces  the  water 
into  the  pores  of  the  wood,  and  makes  it  so  heavy  that 
no  part  of  the  wreck  is  enabled  to  rise  again. 

311  Can  you  sink  a  cork  so  deep  that  it  will  riot  rise  to  the  surfact 
ugain  t 

At  a  great  depth  the  water  forced  by  pressure  into 
the  pores  of  the  cork  renders  it  so  heavy  that  it  cannot 
rise. 

313   What  is  the  pressure  of  water  expressed  in  numbers  f 

The  pressure  of  water  at  any  depth,  whether  on  the 
3* 


SCIENCE   OF  COMMON  THINGS. 


What  is  water  ?  "What  is  hard  water  ? 

sides  of  a  vessel  or  on  its  bottom,  or  on  any  body  im- 
mersed in  it,  is  nearly  one  pound  on  the  square  inch 
for  every  two  feet  of  depth. 

313  What  is  water? 

Water  is  a  fluid  composed  of  oxygen  and  hydrogen, 
in  the  proportion  of  eight  parts  of  oxygen  to  one  part 
of  hydrogen. 

314  Why  is  water  fluid? 

Because  its  particles  are  kept  separate  by  latent 
heat ;  when  a  certain  quantity  of  this  latent  heat  is 
driven  out,  water  becomes  solid,  and  is  called  ice. 

By  increasing  its  latent  heat,  the  particles  of  water  are  again  subdivided 
into  invisible  steam. 

315  Why  is  spring  water  generally  called  "hard  water?", 

Because  it  is  laden  with  foreign  matters,  and  will 
not  readily  dissolve  substances  immersed  in  it. 

316  What  makes  spring  or  well  water  geneartty  hard  ? 

"When  it  filters  through  the  earth,  it  becomes  im- 
pregnated with  sulphate  of  lime,  carbonate  of  lime, 
carbonic  acid,  magnesia,  and  many  other  impurities, 
from  the  earths  and  minerals  with  which  it  comes  in 
contact. 

31 7  What  is  the  cause  of  mineral  springs  ? 

"When  water  trickles  through  the  ground,  it  dissolves 
some  of  the  substances  with  which  it  comes  in  contact ; 
if  these  substances  are  retained  in  solution,  the  water 
will  partake  of  their  mineral  character. 

318  When  is  a  mineral  water  called  a  chalybeate  ? 

When  it  contains  iron,  in  some  form,  dissolved  in  it. 

319  Mineral  springs  exist  in  all  parts  of  our  country :  what  is  the 
nature  of  the  substances  contained  in  them  ? 

The  great  majority  of  them  are  only  impregnated 
with  iron,  salt,  or  sulphur.  Some  few,  however,  con- 
tain many  different  substances,  as  the  mineral  waters 
of  Saratoga. 

3J3O  Why  are  springs  containing  iron  in  large  quantities  beneficial  to 
tome  invalids  ? 

Because  the  iron  contained  in  the  water  acts  as  a 


SCIENCE  OF  COMMON  THINGS.  55 

Purity  of  waters.  Air  in  water.  Do  fishes  breathe  air? 


ionic  j  that  is,  it  strengthens  and  invigorates  the  sys- 
tem. 

331  What  quantity  of  mineral  matter  is  generally  contained  in  com- 
paratively pure  natural  waters  ? 

Any  water  which  contains  less  than  fifteen  grains  of 
solid  mineral  matter  in  a  gallon,  is  considered  as  com- 
paratively pure.  Some  natural  waters  are  known  so 
pure  that  they  contain  only  gV th  of  a  grain  of  mineral 
matter  to  the  gallon,  but  such  instances  are  very  rare. 

Waters  obtained  from  different  sources  may  be  classed  as  regards  com. 
parative  purity  as  follows : 

Rain  water  must  be  considered  as  the  purest  natural  water,  especially 
that  which  falls  in  districts  remote  from  towns  or  habitations;  then 
comes  river  water;  next,  the  water  of  lakes  and  ponds;  next,  spring 
waters  ;  and  then  the  waters  of  mineral  springs.  Succeeding  these,  arc 
the  waters  of  great  arms  of  the  ocean  into  which  immense  rivers  dis- 
charge their  volumes,  as  the  water  of  the  Black  Sea,  which  is  only 
brackish ;  then  the  waters  of  the  ocean  itself;  then  those  of  the  Mediter- 
ranean and  other  inland  seas ;  and  last  of  all,  the  waters  of  those  lakes 
which  have  no  outlet,  as  the  Dead  Sea,  Caspian,  Great  Salt  Lake  of 
Utah,  etc.  etc. 

333  How  much  solid  matter  is  ordinarily  contained  in  a  gallon  of  sea 
water  f 

From  twenty-two  hundred  to  twenty-eight  hundred 
grains. 

333  H<JW  much  solid  matter  is  contained  in  a  gallon  of  water  from  the 
Dead  Sea? 

From  eleven  thousand  to  twenty-one  thousand  grains, 
or  nearly  one-fourth  part  of  its  weight. 

334  Does  air  exist  in  all  natural  waters  f 

It  does :  fishes  and  other  marine  animals  are  depend- 
ent on  the  air  which  water  contains  for  their  existence. 

335  Would  absolutely  pure  water  act  as  a  poison  to  a  fish  f 

The  fish  would  die  of  suffocation  in  such  water. 

336  Where  is  the  purest  water  to  be  found  as  a  natural  product  f 

The  purest  natural  water  that  can  be  procured  is- 
obtained  by  melting  freshly-fallen  snow,  or  by  receiv- 
ing rain  in  clean  vessels  at  a  distance  from  houses. 

337  Why  is  flowing  water  not  liable  to  become  stagnant? 

Because  its  currents  carry  away  all  contaminating 
substances  to  the  sea. 


56  SCIENCE   OF   COMMON   THINGS. 

Spring  water  sparkles.  Eain  water,  why  soft. 

338  What  makes  water  bubble  and  sparkle  f 

The  air  or  gas  contained  in  it. 

339  Why  does  soapy  water,  especially,  lullle  1 

Because  soap  makes  water  tenacious,  and  prevents 
the  bubbles  from  bursting  as  soon  as  they  are  formed. 

330  When  soap-bubbks  are  blown  from  a  pipe,  why  do  they  ascend  f 

Because  they  are  filled  with  the  warm  air  of  the 
lungs,  which  is  lighter  than  cold  air. 

331  Why  is  water  fresh  from  the  well  or  fountain  more  sparkling  and 
refreshing  than  the  same  water  after  it  has  been  for  some  lime  exposed  to 
the  air  ? 

All  spring  and  well  waters  contain  atmospheric  air, 
oxygen,  and  carbonic  acid  gases,  dissolved  in  them. 

The  amount  of  these  substances  contained  in  water,  depends  upon  its 
temperature,  cold  water  dissolving  and  retaining  a  larger  quantity  than 
warm  or  tepid  waters.  When  cold  waters  from  springs  or  fountains  are 
exposed  to  the  air,  they  become  elevated  in  temperature,  and  the  gases 
contained  in  them  escape,  rendering  the  water  flat  and  insipid.  The 
principal  agent  in  imparting  a  sparkle  and  freshness  to  water  is  atmo- 
spheric air,  and  not  carbonic  acid,  as  is  often  supposed  and  taught.  The 
quantity  of  carbonic  acid  present  in  ordinary  spring  waters  is  generally 
inconsiderable. 

333   Why  is  it  difficult  to  wash  with  hard  water  f 

Because  the  water  contains  saline  matters,  which 
deprive  the  water  of  a  part  of  its  solvent  power. 

333   Why  is  it  difficult  to  wash  with  soap  in  salt  water  ? 

Because  soap  is  insoluble  in  salt  water. 

334:    Why  does  water  clean  dirty  linen  f 

Because  it  dissolves  the  stains  as  it  would  dissolve  salt. 

335  Why  does  soap  greatly  increase  the  cleansing  power  of  water  f 

Because  many  stains  are  of  a  greasy  nature  ;  and  the 
alkali  of  the  soap  has  the  power  of  uniting  with  greasy 
matters,  and  rendering  them  soluble  in  water. 

336  Why  is  rain  water  soft  f 

Because  it  is  not  impregnated  with  earths  and  mine* 
rals. 

337  Why  is  it  more  easy  to  wash  with  soft  water  than  with  hard? 

Because  soft  water  ^^nites  freely  with  soap  and  dis- 
solves it ;  in  hard  water  the  soap  is  either  insoluble  01 


SCIENCE   OF   COMMON   THINGS.  57 

Action  of  soap  on  water.  The  sea,  why  salt  ? 

becomes  decomposed.     The   solvent  power  of  water 
increases  also  with  its  purity  or  softness. 

333  When  we  wash  with  soap  in  water  what  chemical  action  takes 
place  ? 

The  soap  is  resolved  into  a  fatty  substance  and  an 
alkali ;  the  alkali  dissolves  most  of  the  organic  sub- 
stances which  constitute  the  dirt  which  we  wish  to 
remove,  and  the  greasy  matter  effects  by  its  lubricity 
an  easy  washing  away  of  the  dissolved  matter  from 
other  substances. 

330   Why  do  wood  ashes  render  hard  water  soft  ? 

Because  they  contain  a  powerful  alkali — potash, 
which  removes  or  neutralizes  those  impurities  in  the 
water  which  rendered  it  hard  and  unfit  for  washing. 

340  Why  does  sugar  or  salt  give  a  flavor  to  water  f 

Because  the  sugar  or  salt  (being  separated  into  very 
minute  particles)  floats  about  in  the  water,  and  mixes 
with  it  intimately. 

341  Why  does  hot  water  dissolve  sugar  and  salt  more  readily  than 
cold  water  t 

Because  the  heat  of  the  water  assists  its  solvent  ac- 
tion, and  opens  for  the  water  a  passage  through  the 
particles  of  the  substance. 

343   Why  is  the  sea  salt  ? 

The  sea  has  undoubtedly  derived  all  its  salt  and 
other  soluble  mineral  substances  by  washings  from 
the  land.  The  streams  that  have  flowed  into  it  for 
ages  have  been  constantly  adding  to  its  quantity,  until 
it  has  acquired  its  present  condition. 

343  Why  is  not  rain  water  salt,  although  most  of  it  is  evaporated 
from  the  sea  f 

Because  salt  will  not  evaporate,  and  therefore  when 
sea  water  is  turned  into  vapor,  its  salt  is  left  behind. 

344  Is  there  more  or  less  of  salt  in  every  spring,  river,  or  lake  ? 

The  saline  condition  of  sea  water  is  but  an  exagge- 
ration of  that  of  all  ordinary  lakes,  rivers,  and  springs  ; 
they  all  contain  more  or  less  of  salt,  but  their  contents 


58  SCIENCE   OF   COMMON  THINGS. 

Salt  lakes.  Effect  of  salt  in  the  ocean.  Mineral  springs. 

are  continually  changing  and  discharging  themselvea 
into  the  sea  ;  therefore  the  salt  does  not  accumulate, 

345  Is  every  lake  into  which  rivers  flow,  and  from  which  there  ts  no 
outlet  except  by  evaporation,  a  salt  lake  f 

It  is  j  and  it  is  curious  to  observe  that  this  condition 
disappears  when  an  artificial  outlet  is  provided  for  such 
waters. 

Such  lakes  are  the  Dead  Sea,  the  Caspian,  the  Sea  of  Aral,  and  the 
Great  Salt  Lake  of  Utah,  the  saltness  of  all  of  which  exceeds  that  of  the 
ocean. 

346  What  good  purposes  does  the  presence  of  so  much  salt  in  the  ocean 
subserve  f 

It  depresses  the  freezing  point  of  the  water  many  de- 
grees, thereby  diminishing  the  dangerous  facility  with 
which  fields  of  ice  are  formed  in  the  polar  regions ;  it 
also  aids  in  preventing  the  corruption  of  the  water  by 
the  accumulation  of  animal  and  vegetable  remains. 

347  What  are  the  substances  extracted  from  the  earth  which  we  find 
in  sea  water  ? 

The  most  abundant  substance  is  common  salt ;  next, 
certain  combinations  of  magnesia  :  then  salts  of  lime, 
with  small  proportions  of  potash,  iron,  iodine,  and  bro- 
mine. 

348  Are  these  substances  found  in  most  springs  f 

With  the  exception  of  iodine  and  bromine,  they  may 
be  found  in  small  quantities  in  almost  all  springs  and 
rivers. 

349  Are  those  substances  which  we  caU  impurities  in  water  of  any  ser- 
vice to  animal  or  vegetable  systems  f       • 

They  give  to  water  its  freshness  and  sparkling  pro- 
perties j  pure  distilled  water  is  very  disagreeable  to 
drink  ;  these  substances  are  also  generally  beneficial  to 
the  systems  of  plants  and  animals,  and  are  absorbed  by 
them  with  the  water. 

350  Does  water  form  part  of  the  composition  of  most  bodies  f 

It  enters  directly  into  the  composition  of  nearly  all 
crystallizdble  bodies  and  most  organic  compounds. 

351  If  the  waters  of  the  ocean  were  not  agitated  by  winds,  currents, 
and  tides,  what  would  be  the  effect  f 


SrfENCE   OF   COMMON   THINGS.  59 


What  are  tides  ?  Cause  of  tides.  High  and  low  tides. 

The  water  would  become  stagnant. 

352  Will  waier  contaminated  with  animal  and  vegetdbk  matter  under 
some  circumstances  purify  itself  f 

Water  contaminated  with  animal  and  vegetable  mat- 
ter, if  kept  for  some  time,  undergoes  a  spontaneous 
purification,  losing  its  offensive  odor  and  color,  and 
depositing  more  or  less  sediment.  "Water,  for  the  sup- 
ply of  ships,  is  well  known  to  undergo  this  process  of 
purification  by  fermentation ;  and  the  larger  the  quan- 
tity of  destructible  matter  suspended  in  it,  the  more 
complete  and  rapid  is  its  purification. 

353  What  is  a  tide  f 

A  tide  is  a  wave  of  tJie  whole  ocean,  which  is  elevated 
to  a  certain  height,  and  then  sinks,  after  the  manner 
of  a  common  wave. 

354  What  te  the  cause  of  tides  f 

The  attraction  of  the  sun  and  moon  upon  the  waters 
of  the  ocean.  The  moon  being  nearest  to  the  earth, 
her  attraction  is  six  times  greater,  than  that  of  the  sun. 
This  attraction  of  the  moon  raises  the  waters  of  the 
ocean  as  they  come  under  her  influence  by  the  motion 
of  the  earth  on  its  axis. 

355  How  many  tides  are  there  in  a  day  f 

Two  in  every  lunar  day — a  period  of  24  hours  49 

minutes. 

350   What  tides  are  the  highest  f 

The  spring  tides. 

357*   Why  are  they  higher  than  at  other  periods  ? 

Because  the  sun  and  moon  are  then  in  such  a  posi- 
tion that  they  exert  their  influence  together.  For  every 
five  feet  of  height  in  tide  produced  by  the  moon,  the 
influence  of  the  sun  adds  one  foot. 

358   What  are  neap  tides  t 

Low  tid.es. 

35Q   Why  are  neap  tides  lower  than  other  tides  f 

Because  then  the  sun  and  moon  have  such  positions 
that  their  attractive  influence  is  opposed  to  each  other  ; 


60  SCIENCE   OF   COMMON   THINGS. 

Tide  movements.  Ebb  a  d  flow.  Sea  waves. 

and  for  every  six  feet  of  the  moon's  tide,  the  opposite 
attraction  of  the  sun  takes  away  one  foot. 

36O  How  fast  does  the  tide  wave  move  f 

The  rate  of  movement  of  the  tide  wave  depends 
upon  the  nature  and  depth  of  the  sea  bottom.  With  a 
depth  of  one  fathom,  its  rate  is  eight  miles  per  hour  ; 
and  with  one  hundred  fathoms,  eighty  miles  per  hour. 

\     361  Does  the  height  of  the  same  tide  vary  in  different  places  f 

The  height  of  the  tide  in  different  places  depends 
much  on  the  configuration  of  the  land  ;  the  same  tide 
may  rise  in  one  place  three  inches,  and  in  another 
place  thirty  feet. 

36S  At  what  period  during  the  day  is  it  high  water  t 

"When  the  moon  passes  the  meridian — that  is,  when 
it  is  nearly  vertical  over  the  place — the  sea  is  elevated 
to  the  greatest  extent,  and  it  is  said  to  be  high  water. 

363  When  is  it  low  water  f 

"When  the  moon  is  upon  the  horizon,  or  about  six 
hours  after  high  tide.  As  the  moon  passes  the  meri- 
dian below  the  horizon,  another  elevation  occurs,  so  that 
we  have  the  ebb  and  flow  of  the  tide  twice  every  day. 

364  How  much  later  does  the  tidal  eHb  and  flow  occur  each  day  f 

The  time  becomes  later  every  day  by  about  fifty 
and  a  half  minutes,  which  is  the  excess  of  a  lunar  day 
above  a  solar  one:  28-J-  minutes  of  the  former  being 
equal  to  27^  minutes  of  the  latter. 

365  What  is  the  cause  of  ordinary  sea  waves  f 

The  wind,  pressing  unequally  on  the  surface  of  the 
sea,  depresses  one  part  more  than  another ;  every  de- 
pression causes  a  corresponding  elevation,  and  these 
undulations  are  called  waves. 

It  must  be  remembered  that  waves  have  no  other  than  a  vertical  m,o- 
tion,  i.e.  up  and  down.  Any  substance,  as  a  buoy,  floating  on  a  wave, 
is  merely  elevated  and  depressed  alternately;  it  does  not  otherwise 
change  its  place. 

366  If  waves  are  stationary,  and  only  move  up  anddmon,  why  do  they 
seem  to  advance  towards  the  shore  f 

This  is  an  ocular  deception.     When  a  corkscrew  is 


SCIENCE   OF   COMMON   THINGS.  61 

Breakers.  Spray  of  waves.  Swr£ 

turned  round,  the  thread  appears  to  move  forward ; 
and  the  apparent  onward  motion  of  the  waves  of  the 
sea  is  a  similar  delusion. 

367  What  is  the  cause  of  breakers  ? 

The  interference  of  rocks  or  rising  ~banks^  in  the  sea 
with  the  regular  form  of  the  wave,  by  which  the  out> 
line  or  curve  of  the  wave  is  broken. 

368  What  causes  the  spray  of  waves  f 

The  wind  driving  the  surface  of  the  water  from  the 
top  of  the  wave,  and  scattering  the  small  particles  in 
all  directions. 

369  What  is  the  surf? 

When  the  shore  runs  out  very  shallow  for  a  great 
extent,  the  breakers  are  distinguished  by  the  name  of 
surf. 

SVO  What  do  we  know  concerning  the  magnitude  and  velocity  of  ocean 
waves  ? 

On  the  Atlantic,  during  a  storm,  the  waves  rise  to  a 
height  of  about  forty-three  feet  above  the  hollow  occu- 
pied by  the  ship  ;  the  total  distance  between  the  crests 
of  two  large  waves  being  559  feet,  which  distance  is 
passed  by  the  wave  in  about  seventeen  seconds  of  time. 

371  With  what  velocity  is  it  estimated  that  such  storm  waves  as  the 
above  described  travel  f 

At  the  rate  of  about  thirty-two  miles  per  hour. 

A  wave  is  a  /orw,  and  not  a  thing ;  the  form  advances,  but  not  the 
substance  of  the  waves. 

3753  If  a  cock  at  the  extremity  of  a  pipe  be  suddenly  closed  while  water 
is  running  through,  why  is  a  noise  and  shock  produced  ? 

Because  the  forward  motion  of  the  whole  body  of 
the  water  contained  in  the  pipe  being  instantly  arrested, 
and  the  momentum  of  a  liquid  being  as  great  as  that 
of  a  solid,  the  water  strikes  the  cock  with  as  much  force 
as  if  it  were  a  long  bar  of  metal,  or  a  rod  of  wood  hav- 
ing  the  same  weight  and  velocity  as  the  water.  Then, 
as  a  fluid  presses  equally  in  all  directions,  a  leaden 
pipe  of  great  length  may  be  widened,  or  even  burst  in 
the  experiment. 


62  SCIENCE   OF   COMMON   THINGS. 

Why  1ce  floats  and  iron  sinks  in  water.  Platinum  and  hydrogen. 


CHAPTER   II. 

SPECIFIC   GRAVITY". 

373  Why  does  ice  float  upon  water  f 

Because  it  is  lighter  than  water. 

374  Why  does  iron  sink  in  water  f 

Because  it  is  heavier  than  water. 

37*5  If  we  put  a  piece  of  ice  in  alcohol,  it  sinks  ;  if  we  put  a  piece,  of 
iron  upon  quicksilver,  it  floats :  why  is  this  f 

Because  the  ice  is  heavier  than  the  alcohol,  and  the 
iron  is  lighter  than  the  quicksilver. 

37*6   What  do  we  mean,  when  we  say  that  ice  is  lighter  than  iron  ? 

We  mean  that,  taking  equal  bulks  of  each,  the  former 
weighs  less  than  the  latter ;  and  when  we  say  that 
quicksilver  is  heavier  than  water,  we  mean  that,  in 
equal  volumes,  as  a  pint,  for  instance,  the  quicksilver 
has  a  greater  weight  than  the  water. 

377  What,  then,  is  specific  gravity  f 

It  is  the  weight  of  a  body  compared  with  the  weight 
of  an  equal  bulk  of  water. 

378  How  does  it  differ  from  ordinary  or  absolute  weight  f 

In  absolute  weight  no  regard  is  paid  to  the  volume  or 
bulk  of  substances.  In  specific  weight,  a  given  bulk 
or  volume  is  compared  with  an  equal  volume  or  bulk 
of  water. 

379  What  body  has  the  greatest  specific  weight  f 

Purified  platina,  which  is  22  times  heavier  than  an 
equal  bulk  of  water. 

380  What  substance  has  tlie  smallest  specific  weight  f 

Hydrogen  gas,  which  is  12,000  times  lighter  than  an 
equal  bulk  of  water. 

381  Why  will  an  egg  float  in  strong  brine,  and  not  in  fresh  water  f 

Because  the  solution  of  a  solid  in  any  liquid  increases 
its  density,  or  its  specific  gravity :  the  addition  of  salt 


SCIENCE   OF   COMMON   THINGS.  63 

Swimming  in  fresh  and  salt  water.  Unskilful  swimmers. 

to  the  water,  renders  the  specific  gravity  of  the  brine 
greater  than  that  of  fresh  water,  or  of  the  egg. 

383  How  do  cooks  sometimes  ascertain  if  their  brine  be  salt  enough  for 
pickling  f 

They  put  an  egg  into  their  brine.  If  the  egg  sinks, 
the  brine  is  not  strong  enough  ;  if  the  egg  floats,  it  is. 

383  Why  witt  an  egg  sink,  if  the  brine  be  not  strong  enough  for  pick- 
ling f 

Because  an  egg  will  be  the  heavier  ;  but  if  as  much 
salt  be  added  as  the  water  can  dissolve,  an  egg  will  be 
lighter  than  the  strong  brine,  and  consequently  float  on 
the  surface. 

384  Why  is  it  more  easy  to  swim  in  the  sea  than  in  a  river  ? 

Because  the  specific  gravity  of  salt  water  is  greater 
than  that  of  fresh ;  and,  therefore,  it  buoys  up  the 
swimmer  better. 

385  Why  do  persons  sink  in  water  when  they  are  unskilful  swimmers? 

Because  they  struggle  to  keep  their  head  out  of  water. 

386  Explain  how  this  is  f 

When  our  head  is  thrown  back  boldly  into  the  water, 
our  mouth  is  kept  above  the  surface,  and  we  are  able 
to  breathe ;  but  when  the  head  is  kept  above  the  sur- 
face of  the  water,  the  chin  and  mouth  sink  beneath  it, 
and  the  swimmer  is  suffocated. 

This  may  be  illustrated  thus : — If  a  piece  of  wood  be  of  such  specific 
gravity  that  only  two  square  inches  can  float  out  of  water,  it  is  manifest, 
that  if  two  other  inches  are  raised  out,  the  two  former  inches  must  be 
plunged  in.  The  body  (in  floating)  resembles  this  piece  of  wood.  If 
two  square  inches  of  our  face  float  out  of  the  water,  we  can  breathe;  but 
if  part  of  the  back  and  crown  of  the  head  are  raised  above  the  water,  the 
lower  part  of  the  face  will  be  depressed  beneath  it. 

387  Why  can  quadrupeds  swim  more  easily  than  man  f 

1.  Because  the  trunk  of  quadrupeds  is  lighter  than 
water,  and  this  is  the  greater  part  of  them  ;  and 

2.  The  position  of  a  beast  (when  swimming)  is  a  na- 
tural one. 

388  Why  is  it  more  difficult  for  a  man  to  swim  than  for  a  beast  f 

1.  Because  his  body  is  more  heavy  in  proportion 
than  that  of  a  beast ;  and 


64:  SCIENCE   OF   COMMON   THINGS. 

How  fishes  ascend  and  descend  in  water.        Life  boats.        Cream  on  milk. 

2.  The  position  and  muscular  action  of  a  man  (when 
swimming)  differ  greatly  from  his  ordinary  habits ;  but 
beasts  swim  in  their  ordinary  position. 

389  Why  can  fat  men  swim  more  easily  than  spare  men? 

Because  fat  is  lighter  than  water  /  and  the  fatter  a 
man  is,  the  more  buoyant  will  he  be. 

390  How  are  fishes  able  to  ascend  to  the  surface  of  water  f 

I  Fishes  have  an  air-bladder  near  the  abdomen ;  when 
this  air-vessel  is  distended,  the  fish  increases  in  size 
and  (being  lighter)  ascends  through  the  water  to  its 
surface. 

391  How  are  fishes  able  to  dive  in  a  minute  to  the  bottom  of  a  stream  f 

They  compress  the  air  in  their  air-bladder  ;  in  conse- 
quence of  which  their  size  is  diminished,  and  they  sink 
instantly. 

393  Why  does  the  body  of  a  drowned  person  rise  and  float  upon  the 
surface  several  days  after  death  ? 

Because,  from  the  accumulation  of  gas  within  the 
body  (caused  by  incipient  putrefaction),  the  body  be- 
comes specifically  lighter  than  water,  and  rises  and 
floats  upon  the  surface. 

393  How  are  life-boats  prevented  from  sinking  ? 

They  contain  in  their  sides  air-tight  cells,  or  boxes 
filled  with  air,  wThich  by  their  buoyancy  prevent  the 
boat  from  sinking  even  when  it  is  filled  with  water. 

394  The  slaves  of  the  West  Indies  have  a  plan  of  stealing  rum  from  a 
cask,  by  inserting  the  long  neck  of  a  bottle,  full  of  water,  through  the  bung. 
How  are  they  enabled  in  this  manner  to  obtain  the  rum  ? 

The  rum  is  very  much  lighter  than  the  water  /  and 
as  the  heavy  water  falls  out  of  the  bottle  into  the  cask, 
the  lighter  rum  rises  to  take  its  place. 

395  Why  does  cream  rise  upon  milk  ? 

Because  it  is  composed  of  particles  of  oily  or  fatty 
matter,  which  are  lighter  than  the  watery  particles  of 
the  milk. 

396  Why  do  stale  eggs  fioat  upon  water? 

Because,  by  keeping,  air  is  substituted  for  a  portion 
of  the  water  of  the  egg,  which  escapes. 


SCIENCE   OF   COMMON  THINGS.  65 


Iron  ships.  Movement  Of  stores  in  water.          Capillary  attraction. 


SOT*  Why  does  not  a  vessel  constructed  of  iron  sink,  as  the  iron  is  much 
heavier  than  the  water  ? 

Because  the  vessel  is  constructed  in  a  concave  form, 
and  is  thus  rendered  buoyant.  Every  substance  be- 
comes lighter  in  water,  in  proportion  to  the  amount  of 
water  displaced.  This  is  a  law  of  nature:  if  it  dis- 
places less  water  than  its  weight  in  air,  it  sinks;  if 
more,  it  floats.  The  ship,  being  concave,  displaces  a 
greater  weight  of  water  than  the  weight  of  the  iron  of 
which  it  is  composed  in  the  air. 

A  thick  piece  of  iron,  weighing  half  an  ounce,  loses  in  water  nearly 
one-eighth  jf  its  weight ;  but  if  it  is  hammered  out  into  a  plate  or  vessel, 
of  such  a  size  that  it  occupies  eight  times  as  much  space  as  before,  it  then 
loses  its  whole  weight  in  water,  and  will  float,  sinking  just  to  the  brim. 
If  made  twice  as  large,  it  will  displace  one  ounce  of  water,  consequently, 
twice  its  own  weight ;  it  will  then  sink  to  the  middle,  and  can  be  loaded 
with  half  an  ounce  weight  before  sinking  entirely. 

398  Why  are  stones,  gravel,  and  sand  so  easily  moved  by  waves  and 
currents  ? 

Because  the  moving  water  has  only  to  overcome 
about  half  the  weight  of  the  stone. 

399  Why  can  a  stone  which,  on  land,  requires  the  strength  of  two  men 
to  lift  it,  be  lifted  and  carried  in  water  by  one  man  f 

Because  the  water  holds  up  the  stone  with  a  force 
equal  to  the  weight  of  the  volume  of  water  it  displaces. 


CHAPTER   III. 

CAPILLARY   ATTRACTION. 

400  Why  does  water  melt  salt  ? 

Because  very  minute  particles  of  water  insinuate 
themselves  into  the  pores  of  the  salt  by  capillary  at- 
traction, and  force  the  crystals  apart  from  each  other. 

401  Why  does  water  melt  sugar  f 

Because  very  minute  particles  of  water  insinuate 


66 


SCIENCE   OF   COMMON   THINGS. 


"Watering  plants.  Cotton  lamp-wick. 


Blotting  paper  absorbs  ink. 


fig.  18. 


themselves  into  the  pores  of  the  sugar  by  capillary 
attraction*  and  force  the  crystals  apart  from  each 
other. 

4OS   What  is  capillary  attraction  ? 

The  power  which  very  minute 
tubes  possess  of  causing  liquid  to 
rise  in  them  above  its  level. 

"  Capillary,"  from  the  Latin  word,  "  capil- 
laris"  (like  a  hair) ;  the  tubes  referred  to  are 
almost  as  fine  and  delicate  as  a  hair.  Water 
ascends  through  a  lump  of  sugar  or  «pieee  of 
sponger  by  capillary  attraction. 

N.  B.  The  smaller  the  tube,  the  higher  will 
the  liquid  be  attracted  by  it.  Fig.  18  illus- 
trates the  manner  in  which  water  will  rise  in 
tubes  of  different  diameters. 

403  Why  is  vegetation  on  the  margin  of  a  river  more  luxuriant  than 
in  an  open  field  ? 

Because  the  porous  earth  on  the  bank  draws  up  too-. 
ter  to  the  roots  of  the  plants  by  capillary  attraction. 

404  Why  do  persons  who  water  plants  very  often  pour  the  water  into 
the  saucer,  and  not  over  the  plants  ? 

Because  the  water  in  the  saucer  is  drawn  up  by  the 
mould  (through  the  hole  at  the  bottom  of  the  flower- 
pot), and  is  transferred  to  the  stem  and  leaves  of  the 
plant  by  capillary  attraction. 

405  Why  is  cotton  best  adapted  for  lamp-wicks  f 

Because  the  arrangement  of  the  fibres  of  the  cotton- 
wick  is  such,  that  the  whole  forms  a  bundle  of  minute 
tubes,  in  which  the  oil  ascends  and  supplies  the  flame 
by  capillary  attraction. 

406  Why  does  blotting-paper  absorb  ink  f 

The  ink  is  drawn  up  between  the  minute  fibres  of 
the  paper  by  capillary  attraction. 

407  Why  will  not  writing  or  sized  paper  absorb  ink  f 

Because  the  sizing,  being  a  species  of  glue  into 
which  writing  papers  are  dipped,  fills  up  the  little  in' 
terstices  or  spaces  between  the  fibres,  ana  in  this  way 
prevents  all  capillary  attraction. 

408  How  does  a  sponge  absorb  water  t 


SCIENCE   OF   COMMON    THINGS.  67 

Dry  wood  swells  in  water.        Solution  of  substances.         Liquids  and  gases. 

The  pores  of  the  sponge  constitute  minute  tubes  in 
which  the  water  rises  by  capillary  attraction. 

409  Why  does  dry  wood,  immersed  in  water,  swell  1 

Because  the  water  enters  the  pores  of  wood  by  capil- 
lary attraction,  and  forces  the  particles  further  apart 
from  each  other. 

41 0  Why  does  sugar  or  salt  give  a  flavor  to  water  f 

Because  the  sugar  or  salt  (being  separated  into  very 
minute  particles)  floats  about  the  water,  and  mixes 
with  it  intimately. 

411  Why  does  hot  water  dissolve  sugar  and  salt  more  readily  than  cold 
water  f 

Because  the  heat  of  the  water  assists  its  solvent  ac- 
tion, and  opens  for  the  water  a  passage  through  the 
particles  of  the  substance. 


CHAPTEK    IT. 

THE    GENERAL   PROPERTIES    OF   AERIFORM    OR    GASEOUS 
BODIES. 

413   What  is  the  difference  between  a  liquid  and  a  gas? 

The  distinction  between  liquids  and  those  more  elas- 
tic fluids  which  wre  term  air,  gas,  vapor,  steam,  etc., 
depends  principally  on  heat  and  pressure.  Thus,  wa- 
ter, according  to  the  addition  or  subtraction  of  heat, 
may  exist  as  a  solid,  ice ;  as  a  liquid,  wrater ;  or  as  a 
vapor,  steam. 

413  Under  what  pressure  of  the  atmosphere  is  water  converted  into 
steam  ? 

Tinder  the  ordinary  pressure  of  the  atmosphere,  wa- 
ter is  converted  into  steam  at  212  degrees,  Fahrenheit's 
thermometer ;  if  this  pressure  is  increased,  it  requires 


68  SCIENCE   OF   COMMON   THINGS. 

Varieties  of  gaseous  bodies.        Composition  of  the  atmosphere.        Air  porous. 

a  proportionally  higher  temperature  ;  if  this  pressure 
is  diminished,  the  amount  of  heat  required  is  propor- 
tionably  less. 

414  How  many  kinds  of  aeriform  or  gaseous  bodies  exist  in  nature  f 

Those  which,  under  common  circumstances  of  tem- 
perature and  pressure,  are  always  in  a  gaseous  state, 
as  common  air ;  and  those  which  become  gases  chiefly 
at  high  temperature,  as  steam,  or  vapor  of  water. 

415  Are  all  gases  invisible  or  colorless  like  atmospheric  air  f 

Some  gases  possess  color,  but  the  greater  number 
are  colorless  and  invisible. 

416  Of  what  is  atmospheric  air  composed  f 

Principally  of  two  gases,  oxygen  and  nitrogen,  mixed 
together  in  the  following  proportion  :  viz.  one  volume 
of  oxygen  to  four  of  nitrogen. 

It  must  not  be  forgotten  that  the  air  contains  small  quantities  of  other 
gaseous  substances  also,  as  vapor  of  water,  carbonic  acid,  and  ammonia. 

41 7*  Do  the  particles  of  which  atmospheric  air  and  other  gaseous  bodies 
are  composed,  appear  to  have  any  cohesion  between  themselves  f 

The  ultimate  particles  of  which  air  and  other  gases 
are  composed  appear  to  be  destitute  of  cohesion  ;  hence 
air  has  a  disposition  not  only  to  sink  down  and  spread 
out  laterally,  like  liquids  when  unconfined,  but  also  to 
expand  and  rise  upwards. 

418  Is  the  air  porous  f 

Yes  ;  in  a  very  high  degree. 

419  How  do  we  know  this  fact  ? 

Because  air  readily  yields  to  pressure,  and  a  great 
bulk  of  it  may  be  forced  to  occupy  a  very  small  space. 

4SO  Is  air  also  impenetrable  f 

Yes ;  beyond  a  certain  limit  it  cannot  be  compressed. 

431  How  much  lighter  is  steam  than  ordinary  air  f 

Steam  has  but  little  more  than  half  the  weight  of 
atmospheric  air  ;  and  hence  it  rises  and  floats  in  the 
air  as  a  cork  rises  and  floats  in  water. 


SCIENCE   OF   COMMON   THINGS.  69 

What  is  the  atmosphere  ?  Why  mountains  appear  blue. 


CHAPTEE   Y. 

THE   ATMOSPHERE. 

433   What  do  we  understand  by  the  atmosphere  f 

The  thin  transparent  fluid  which  surrounds  the  earth 
to  a  considerable  height  above  its  surface,  and  which, 
by  its  peculiar  constitution,  supports  animal  life  by 
respiration,  and  is  also  necessary  for  the  due  exercise 
of  the  vegetable  functions. 

433  Is  the  atmosphere  invisible  f 

It  is  generally,  but  erroneously,  so  regarded.  The 
atmosphere  is  not  invisible. 

434  How  can  you  prove  that  the  atmosphere  is  not  invisible  f 

Because  when  we  look  upwards  into  the  firmament  on 
a  clear  day,  the  space  appears  of  an  azure  or  clear  color. 

This  color  belongs  not  to  anything  which  occupies  the  space  in  which 
the  stars  or  other  celestial  objects  are  placed,  but  to  the  mass  of  .air 
through  which  the  bodies  are  seen. 

435  Why  do  distant  mountains  appear  Hue  f 

"Not  because  it  is  their  color,  but  because  it  is  the 
color  of  the  air  through  which  they  are  seen. 

-±36  Has  air  weight  f 

It  has  /  as  well  as  lead,  stone,  or  any  other  material 
substance. 

437  How  can  this  be  readily  proved? 

By  weighing  a  vessel  filled  with  air,  and  the  same 
vessel  after  the  air  has  been  exhausted  from  it. 

438  Can  the  existence  of  air  be  known  by  the  sense  of  touch  or  feeling  f 

It  can  ;  since  it  opposes  resistance  when  acted  upon, 
and  strikes  with  a  force  proportionate  to  the  speed  of 
its  motion. 

438  Why  do  we  always  feel  a  breeze  on  the  deck  of  a  steamboat  in 
motion,  even  upon  the  calmest  day  t 

Because  our  bodies  forcibly  displace  the  air  as  w$ 
are  carried  through  it, 

4 


70  SCIENCE   OF   COMMON   THINGS. 

Height  of  the  atmosphere.  Weight  of  the  atmosphere. 

430  How  are  waves  of  the  ocean  produced  ? 

By  the  force  of  the  air  in  motion,  or  wind  striking 
upon  the  surface  of  the  water. 

431  Could  a  bird  fly  in  a  space  devoid  of  air,  even  if  it  could  exist 
without  respiration  ? 

It  could  not ;  as  the  bird  rises  simply  by  the  resist- 
ance of  the  particles  of  air  to  the  beating  of  its  wings. 

/    432  How  do  we  know  that  air  is  elastic  f 

Because  a  volume  of  compressed  air,  the  pressure 
being  removed,  immediately  restores  itself  to  its  origi- 
nal bulk. 

433  When  is  air  said  to  be  rarefied  f 

When  a  given  quantity  of  air  is  caused  to  expand 
and  occupy  a  greater  space,  it  is  said  to  be  rarefied. 

"When  a  part  of  the  air  inclosed  in  any  vessel  is  withdrawn,  that  which 
remains,  expanding  by  its  elastic  property,  always  tills  the  dimensions  of 
the  vessel  as  completely  as  before.  If  nine-tenths  were  withdrawn,  the 
remaining  one-teiith  would  occupy  the  same  space  that  the  whole  did 
formerly. 

434  What  is  the  height  of  the  atmosphere  above  the  surface  of  the  earth  f 

It  is  supposed  to  be  about  45  miles  ;  the  zone  or  shell 
of  air  which  surrounds  the  earth  to  the  height  of  nearly 
21  miles  from  its  surface,  contains  one-half  of  the 
atmosphere ;  and  the  remaining  half  being  relieved  of 
this  superincumbent  pressure,  expands  into  another 
zone  or  belt  of  the  thickness  of  41  or  42  miles. 

Some  authorities  suppose  this  last  zone  to  have  a  much  greater  area. 

435  What  is  the  weight  of  air  compared  with  that  of  water  f 

Water  is  about  840  times  the  weight  of  air,  taken 
l>ulkfor  bulk. 

430  What  is  the  estimated  weight  of  the  whole  atmosphere  enveloping 
tJie  globe  f 

To  the  weight  of  a  globe  of  lead  sixty  miles  in  dia- 
meter. 

437'  As  air  has  weight,  and  as  the  mass  of  it  extends  at  least  45  miles 
above  the  earths  surface,  what  amount  of  pressure  does  it  exert  ? 

At  the  level  of  the  ocean  the  atmosphere  exerts  a 
pressure  of  about  1 5  pounds  for  every  square  inch  of 
surface. 


SCIENCE   OF   COMMON   THINGS.  71 

Pressure  of  air.  Vacuum. 


438  If  the  air  were  condensed,  so  as  to  occupy  no  more  space  than  the 
same  weight  of  water,  to  how  great  an  tkvation  above  the  earth  would  it 

extend  ? 

To  an  elevation  of  thirty-four  feet. 

439  In  what  direction  is  the  pressure  of  the  atmosphere  exerted  f 

It  is  the  nature  of  a  fluid  to  transmit  pressure  in  every 
direction  equally  ;  therefore  the  air  presses  upwards, 
downwards,  laterally,  and  obliquely,  with  the  same 
force. 

440  How  great  a  pressure  is  exerted  by  the  air  upon  the  body  of  a 
man  or  animal  having  a  surface  of  2000  square  inches  f 

Not  less  than  30,000  pounds,  or  about  15  tons. 

441  Why  is  not  the  individual  crushed  beneath  so  enormous  a  load? 

Because  the  atmosphere  presses  equally  in  all  direc- 
tions^ and  our  bodies  are  filled  with  liquids  capable  of 
sustaining  pressure,  or  with  air  of  the  same  density  as 
the  external  air ;  so  that  the  external  pressure  is  met 
and  counteracted  by  the  internal  resistance. 

44S  What  would  be-  the  effect  upon  a  man  or  animal  if  at  once 
relieved  of  all  atmospheric  pressure  ? 

All  the  blood  and  fluids  of  the  body  would  be  forced 
~by  expansion  to  the  surface,  and  the  animal  would  burst. 

443  What  do  we  mean  by  a  vacuum? 

A  space  devoid  of  all  matter ;  in  general,  we  mean 
by  a  vacuum,  a  space  devoid  of  air. 

444  Can  a  perfect  vacuum  be  produced  artificially  f 

No ;  but  confined  spaces  may  be  deprived  of  air 
sufficiently  for  all  experimental  or  practical  purposes. 

445  Are  there  any  instances  of  a  vacuum  in  nature? 

There  is  no  positive  certainty  that  the  spaces  which 
exist  between  the  various  planets  and  other  hea- 
venly bodies,  are  occupied  with  any  material  sub- 
stance. 

446  Is  the  existence  of  air  necessary  to  the  production  of  sound? 

It  is ;  in  a  vacuum  there  can  be  no  sound  ;  and  on 
the  top  of  high  mountains,  where  the  air  is  greatly 
rarefied,  as  on  Mont  Blanc,  the  report  of  a  pistol  can 
hardly  be  heard. 


72  SCIENCE   OF   COMMON   THINGS. 

How  flies  walk  on  the  ceiling.  How  we  breathe. 


447*  Why  is  it  often  painful  and  difficult  to  breathe  on  a  mountain-top  f 

Because,  owing  to  the  extreme  rarity  of  the  air  on 
the  top  of  the  mountain,  a  person,  although  expanding 
his  chest  as  much  as  usual,  really  takes  in  only  half 
as  much  air  as  he  does  when  at  the  foot  of  the  moun- 
tain. 

448  If  the  lips  be  applied  to  the  back  of  the  hand,  and  the  breath  drawn 
in  so  as  to  produce  a  partial  vacuum  in  the  mouth,  why  will  the  skin  be 
drawn  or  sucked  in  f 

Not  from  any  force  resident  in  the  lips  or  the  mouth 
drawing  the  skin  in,  but  from  the  fact  that  the  usual 
external  pressure  of  air  is  removed,  and  that  the  pres- 
sure from  within  the  skin  is  suffered  to  prevail. 

449  How  is  a  boy  enabled  to  lift  a  stone  by  means  of  the  common 
sucker  ? 

The  sucker  consists  of  a  disk  of  moistened  leather, 
with  a  string  by  which  it  may  be  suspended  with  any 
weight  attached  to  it.  If  its  smooth  moist  surface  be 
pressed  so  closely  against  the  flat  side  of  a  stone  or 
other  body  that  the  air  cannot  enter  between  them,  the 
weight  of  the  atmosphere  pressing  upon  the  upper  sur- 
face of  the  leather  makes  it  adhere  so  strongly,  that  a 
stone  of  weight  proportioned  to  the  extent  of  the  disk 
of  leather  may  be  raised  by  lifting  the  string. 

450  How  are  flies  and  other  small  insects  enabled  to  walk  on  ceilings 
and  surfaces  presented  downwards,  or  upon  smooth  panes  of  glass  in  an 
upright  position  ? 

Their  feet  are  formed  in  such  a  manner  that  they 
act  as  small  air-pumps  or  suckers,  excluding  the  air 
between  them  and  the  surface  with  which  they  are  in 
contact ;  and  the  atmospheric  pressure  keeps  the  animal 
in  position. 

451  Why  in  breathing  do  we  first  draw  in  the  breath,  as  it  is  termed? 

Because  by  so  doing  we  make  an  enlarged  space  in 
the  chest,  and  the  pressure  of  the  external  atmosphere 
forces  the  air  in  to  fill  it. 

The  air  enters  the  lungs,  not  because  they  draw  it  in,  but  by  the  weight 
of  the  atmosphere  forcing  it  into  an  empty  space. 

453  How  is  the  air  caused  to  escape  from  the  lungs  f 

Simply  by  means  of  its  elasticity  ;    the  lungs  by 


SCIENCE   OF   COMMON   THINGS.  73 

Why  a  jug  gurgles.  Air  in  water. 

muscular  action  compress  the  air  contained  in  them, 
and  give  to  it  by  compression  a  greater  elasticity  than 
the  air  without.  By  the  excess  of  the  elasticity  it  is 
propelled,  and  escapes  by  the  mouth  and  nose. 

453  Why  does  a  bottle  or  jug  gurgle  when  liquid  is  freely  poured 
from  it  ? 

On  account  of  the  pressure  of  the  atmosphere  forcing 
air  into  the  interior  of  the  bottle.  In  the  first  instance, 
the  neck  of  the  bottle  is  filled  with  liquid,  so  as  to  stop 
the  admission  of  air.  When  a  part  has  flowed  out,  and 
an  empty  space  is  formed  within  the  bottle,  the  atmo- 
spheric pressure  forces  in  a  bubble  of  air  through  the 
liquid  in  the  neck,  which,  by  rushing  suddenly  into  the 
interior  of  the  bottle,  produces  the  sound.  . 

454  How  long  will  a  lottle  continue  to  gurgle  ? 

/So  long  as  the  neck  continues  to  be  choked  with  liquid. 
But  as  the  contents  of  the  bottle  are  discharged,  the  - 
liquid,  in  flowing  out,  only  partially  fills  the  neck  ;  and, 
while  a  stream  passes  out  through  the  lower  half  of  the 
neck,  a  stream  of  air  passes  in  through  the  upper  part. 
The  flow  being  now  continued  and  uninterrupted,  no 
sound  takes  place. 

455  Does  air  exist  in  water  f 

Water,  and  most  liquids  exposed  to  the  air,  absorb  a 
greater  or  less  quantity r,  which  is  maintained  in  them  by 
the  pressure  of  the  atmosphere  acting  on  the  surface. 

456  Why  is  boiled  water  flat  and  insipid  f 

Because  the  agency  of  the  heat  expels  the  &ir  which 
the  water  previously  contained. 

457*  Could  fishes  and  other  marine  animals  live  in  water  deprived  of 
air  ? 

They  could  not,  as  they  breathe  the  air  contained  in 
the  water. 

458  Why  do  ale,  porter,  and  cider  froth,  and  champagne  sparkle,  when 
uncorked  and  poured  into  an  open  vessel  f 

When  these  liquors  are  bottled,  the  air  confined 
under  the  cork  is  condensed,  and  exerts  upon  the  sur- 
face a  pressure  greater  than  that  of  the  atmosphere. 


SCIENCE   OF  COMMON   THINGS. 


Frothing  of  ale.  Sparkling  of  champagne.  Meteorology. 

This  has  the  effect  of  holding,  in  combination  with  the 
liquor,  air  or  gas  which,  under  the  atmospheric  pressure 
only,  would  escape.  If  any  air  or  gas  rise  from  the 
liquor  after  being  bottled,  it  causes  a  still  greater  con- 
densation, and  an  increased  pressure  above  its  surface. 
When  the  cork  is  drawn  from  a  bottle  containing  liquor 
of  this  kind,  the  air  fixed  in  the  liquid,  being  released 
from  the  pressure  of  the  air  which  was  condensed  under 
the  cork,  instantly  makes  its  escape,  and,  rising  in 
bubbles,  produces  effervescence  and  froth. 

459  Why  do   bottles  containing  ale,  cider,  porter,  &c.,   frequently 
burst  f 

It  is  the  nature  of  these  liquids  to  produce  gas  or  air 
in  considerable  quantities,  the  elastic  force  of  which 
sometimes  becomes  greater  than  the  cohesive  strength 
of  the  particles  of  matter  composing  the  bottle,  which 
then  necessarily  gives  way,  or  bursts. 

460  Why  does  one  kind  of  liquor  froth,  and  another  kind  only  sparkle,  f 

Those  liquors  only  which  are  viscid,  glutinous,  or 
thick,  froth,  because  they  retain  the  little  bubbles  of 
air  as  they  rise  ;  while  a  thin  liquor,  like  champagne, 
suffers  the  bubbles  to  escape  readily. 


CIIAPTEK   VI. 

ATMOSPHERICAL   PHENOMENA. 

461  What  designation  do  we  give  to  that  department  of  science  which 
treats  of  the  various  phenomena  of  the  atmosphere? 

Meteorology. 

463  How  is  the  air  heated  f 

In  two  ways ;  either  by  the  rays  of  the  sun  passing 
through  it,  or  by  the  heat  communicated  to  it  by  the 
earth. 


SCIENCE   OF   COMMON  THINGS;  75" 

Air,  how  heated  and  cooled.  Origin  of  winds. 

463  In  what  manner  is  the  air  heated  by  the  earth  ? 

The  sun  heats  the  earth,  and  the  earth  heats  the  air 
resting  upon  it ;  the  air  thus  heated  rises,  and  is  suc- 
ceeded by  other  air,  which  is  heated  in  a  similar  way, 
till  the  whole  volume  is  warmed, 

464  How  is  the  air  made  cold? 

The  air  resting  on  the  earth  is  made  cold  by  contact  / 
this  cold  air  makes  the  air  above  it  cold  /  and  cold  cur- 
rents (or  winds)  cause  the  whole  to  mix  together,  until 
all  becomes  of  one  temperature. 

465  What  effect  is  produced  upon  air  "by  cold  f 

It  is  condensed  or  compacted  into  a  smaller  compass ; 
in  consequence  of  which  it  becomes  heavier,  and  de- 
scends towards  the  ground. 

466  Prove  that  the  air  is  condensed  ly  cold. 

Lay  a  bladder  half  full  of  air  before  a  fire,  till  it  has 
become  inflated  ;  if  it  be  now  removed  from  the  fire$ 
the  bladder  will  collapse  again,  because  the  air  con- 
denses into  its  former  bulk. 

467  What  effects  has  heat  upon  air  f 

Heat  rarefies  or  makes  it  lighter ;  that  is,  a  quantity 
of  air  heated  will  occupy  more  space  than  the  same 
quantity  which  has  been  cooled. 

468  What  is  wind  f 

"Wind  is  air  put  in  motion. 

460    What  occasions- those  movements  of  the  air  which  we  call  wind? 

The  principal  cause  is  the  variation  of  temperature 
produced  by  the  alternation  of  day  and  night  and  the 
succession  of  the  seasons. 

4"7O  How  can  winds  originate  through  variations  of  temperature  f        { 

"When  through  the  agency  of  the  sun  a  particular 
portion  of  the  earth's  surface  is  heated  to  a  greater 
degree  than  the  remainder,  the  air  resting  upon  it 
becomes  rarefied  and  ascends,  while  a  current  of  cold 
air  rushes  in  to  supply  the  vacancy.  Two  currents,  the 
one  of  warm  air  flowing  out,  and  the  other  of  cold  air 
flowing  in,  are  thus  continually  produced ;  and  to  these 


76  SCIENCE   OF   COMMON   THINGS. 


"Wind  always  blows.  Effect  of  mountains  on  winds. 

movements  of  the  atmosphere  we  apply  the  designation 
of  wind. 

471  Does  the  wind  always  blow  f 

Yes  ;  there  is  always  some  motion  in  the  air ;  but  the 
violence  of  the  motion  is  perpetually  varying. 

473  Does  the  rotation  of  the  earth  upon  its  axis  affect  the  motion  of 
the  air  f 

1  Yes,  in  two  ways :  1.  As  the  earth  moves  round  its 
axis,  the  thin  movable  air  is  left  somewhat  behind,  and 
therefore  seems  (to  a  stationary  object)  to  be  blowing 
in  the  opposite  direction  to  the  earth's  motion ;  and 

2.  As  the  earth  revolves,  different  portions  of  its  sur- 
face are  continually  passing  under  the  vertical  rays  of 
the  sun. 

473  When  are  the  rays  of  the  sun  called  vertical  rays  ? 

When  the  sun  is  in  a  direct  line  above  any  place,  his 
rays  are  said  to  be  "vertical "  to  that  place. 

474  When  the  sun  is  vertical,  or  nearly  over  head  at  any  place,  what 
time  of  day  is  it  at  that  place  ? 

Noon. 

475  How  does  a  change  in  the  heat  of  air  produce  wind  f 

The  air  always  seeks  to  preserve  an  equilibrium  •  so 
cold  air  rushes  into  the  void  made  by  the  upward  cur- 
rent of  warm  air. 

470  Why  does  not  the  wind  always  blow  one  way,  following  the  direc- 
tion of  the  sun  f 

Because  the  direction  of  the  wind  is  subject  to  per- 
petual interruption  from  kills  and  valleys,  deserts, 
seas,  &c. 

477  How  can  hills  or  mountains  affect  or  change  the  direction  and  course 
of  the  wind  ? 

If  a  current  of  air,  blowing  from  a  particular  direc- 
tion, strike  against  the  side  of  a  mountain,  it  will  neces- 
sarily be  deflected  from  a  straight  line,  and  must  either 
ascend  the  mountain,  turn  back,  or  assume  a  lateral 
direction. 

478  Why  are  those  winds  which  llow  over  large  continents  or  tracts 
of  land  generally  dry  ? 


SCIENCE  OF  COMMON  THINGS.  7< 

Velocity  of  winda.  Force  of  winds. 

Because  in  their  passage  they  absorb  very  little  water, 
as  they  do  not  blow  over  large  oceans. 

479  Why  do  our  "hands  and  lips  chap  in  frosty  and  windy  weather  1 

Because  a  cold,  dry  wind  absorbs  moisture  from  the 
surface  of  the  skin  ;  and  this  action,  in  turn,  causes  the 
skin  to  crack  and  inflame. 

480  Would  the  wind  blow  regularly  from  east  to  west  if  all  obstructions 
were  removed  ? 

Without  doubt.  If  the  whole  earth  were  covered 
with  water,  the  winds  would  always  follow  the  sun, 
and  blow  uniformly  in  one  direction. 

481  Do  winds  ever  blow  regularly  f 

Yes,  in  those  parts  of  the  world  which  present  a 
large  surface  of  water,  as  in  the  Atlantic  and  Pacific 
Oceans. 

483    With  what  velocity  do  winds  move  f 

Every  graduation  exists  in  the  speed  of  winds,  from 
the  mildest  zephyr  to  the  most  violent  hurricane. 

483  With  what  velocity  does  a  wind  which  is  hardly  perceptible  move  f 

With  a  velocity  of  about  one  mile  per  hour,  and 
with  a  perpendicular  force  on  one  square  foot  of  *005 
Ibs.  avoirdupois. 

484  In  a  gentle  wind,  what  is  the  velocity  and  estimated  pressure  f 

'From  four  to  Jive  miles  per  hour,  and  a  force  of  "079 
to  123  Ibs.* 

485  In  a  very  brisk  wind,  what  is  the  velocity  and  pressure  ? 

From  twenty  to  twenty -free  miles  per  hour  /  force  1*9 
to  3-07  Ibs. 

4SQ   What  is  the  velocity  and  pressure  of  the  wind  in  a  storm  t 

From  fifty  to  sixty  miles  per  hour,  with  a  pressure 
of  7  to  12  Ibs. 

487  In  a  hurricane,  what  is  the  estimated  velocity  and  pressure  f 

From  eighty  to  one  hundred  miles  per  hour>  with  a 
varying  force  of  31  to  50  Ibs. 

*  In  these  estimates  the  pressure  is  computed  per  square  foot  in 
pounds  avoirdupois. 


78  SCIENCE   OF   COMMON   THINGS. 

Movements  of  clouds.  Trade  winds  and  their  location. 

488  Why  do  we  sometimes  see  clouds  at  one  elevation  moving  in  one 
direction,  and  at  anotfier  elevation,  at  the  same  time,  others  moving  in  a 
contrary  direction  ? 

Because  different  currents  of  air  exist  at  different 
elevations,  moving  in  different  airections,  with  different 
velocities. 

In  1839,  an  English  aeronaut,  at  the  height  of  14,000  feet,  encountered 
a  current  that  bore  him  along  at  the  rate  of  five  miles  per  hour ;  but, 
upon  descending  to  the  altitude  of  12,000  feet,  he  met  with  a  contrary- 
wind,  blowing  with  a  velocity  of  eighty  miles  per  hour. 

489  How  is  the  force  of  the  wind  ascertained  ? 

By  observing  the  amount  of  pressure  that  it  exerts 
upon  a  given  plane  surface  perpendicular  to  its  own 
direction. 

If  the  pressure  plate  acts  freely  upon  spiral  springs,  the  power  of  the 
wind  is  denoted  by  the  extent  of  their  compression,  and  that  weight  will 
be  a  measure  of  their  force,  the  same  as  in  weighing  by  the  ordinary 
spring-balance. 

09 O  What  is  an  instrument  for  measuring  the  force  of  the  wind  called  f 

An  Anemometer. 

491  What  are  the  constant  winds  which  bloiv  over  the  Atlantic  and 
Pacific  Oceans  called  f 

They  are  called  "  trade-winds" 

493   Why  are  they  called  trade-winds  f 

Because  they  are  very  convenient  to  navigators  who 
have  to  cross  the  ocean,  inasmuch  as  they  always  blow 
in  one  direction. 

493  In  what  direction  do  the  trade-winds  blow  f 

That  in  the  northern  hemisphere  blows  from  the 
north-east ;  that  in  the  southern  hemisphere  from  the 
south-east. 

494  Do  trade-winds  blow  from  the  north-east  and  south-east  all  Hie 
year  round  1 

Yes,  in  the  open  sea;  that  is  in  the  Atlantic  and 
Pacific  oceans,  for  about  25°  each  side  of  the  equator. 

495  Where  do  the  trade-winds  blow  with  uniform  force  and  constancy  f 

In  many  parts  of  the  Pacific  embraced  within  the 
region  of  the  trade-winds,  a  vessel  may  sail  for  a  week 
without  altering  the  position  of  a  sail  or  rope. 


SCIENCE   OF   COMMON   THINGS.  79 

Cause  of  sea  breezes.  North  and  south  winds. 

406  Why  does  a  sea  breeze  feel  cool  f 

Because  the  sun  cannot  make  the  surface  of  the  sea 
so  hot  as  the  land  ;  therefore  the  air  which  blows  from 
the  sea  is  cooler  than  the  air  of  the  land. 

407  Why  is  there  generally  a  fresh  breeze  from  the  sea  during  ihe 
summer  and  autumn  mornings  f 

Because  land  is  more  heated  by  the  sun  than  the  sea 
is  ;  and  the  land  air  becomes  hotter  than  that  over  the 
sea ;  in  consequence  of  which  the  cooler  sea  air  glides 
inland  to  restore  the  equilibrium. 

408  Why  are  ihe  west  winds  in  the  Atlantic  States  generally  dry? 

Because  they  come  over  large  tracts  of  land,  and 
therefore  absorb  very  little  water  ;  and  being*  thirsty, 
they  readily  imbibe  moisture  from  the  air  and  clouds, 
and  therefore  bring  dry  weather. 

400   Why  is  the  north  wind  generally  coldf 

Because  it  comes  from  the  polar  regions,  over  moun- 
tains of  snow  and  seas  of  ice. 

500  Why  are  north  winds  generally  dry  ? 

Because  they  come  from  colder  regions,  and  being 
warmed  by  the  heat  of  our  climate,  absorb  moisture 
from  everything  they  touch  ;  in  consequence  of  which 
they  are  generally  dry. 

501  Why  are  south  winds  generally  warm  f 

Because  they  come  over  countries  warmer  than  our 
own,  where  they  are  much  heated. 

SOS  Why  are  winds  which  blow  over  a  vast  body  of  water  generally  rainy  f 

Because  they  come  laden  with  vapor ;  if,  therefore, 
they  meet  with  the  least  chill,  some  of  the  vapor  is 
deposited  as  rain. 

SOS    Why  is  there  often  an  evening  breeze  during  the  summer  months  9 

Because  the  earth  radiates  heat  at  sunset,  and  the 
air  is  rapidly  cooled  down  by  contact;  this  conden- 
sation causes  a  motion  in  the  air,  called  the  evening 
breeze. 

SO4   Why  do  south  winds  often  bring  rain  f 

Because,  coming  from  the  torrid  zone,  they  are  much 


80  SCIENCE   OF   COMMON   THINGS. 

Effect  of  the  winds  on  the  weather.  Hurricanes. 


heated,  and  absorb  water  very  plentifully  as  they  pass 
over  the  ocean. 

SOS  How  does  this  account  for  the  rainy  character  of  south  winds  f 

As  soon  as  they  reach  a  cold  climate  they  hecome 
chilled,  and  can  no  longer  hold  all  their  vapor  in  sus- 
pension ;  in  consequence  of  which  some  of  it  is  deposited 
as  rain. 

SOG  Why  are  dry  winds  in  the  spring  montJis  desirable  and  advan* 
tageous  for  agricultural  operations  f 

They  dry  the  soil  saturated  with  the  moisture  ot 
winter,  'break  up  the  heavy  clods,  and  fit  the  land  for 
the  seed  committed  to  it. 

SOT*   Why  is  a  fine  clear  day  sometimes  overcast  in  a  few  minutes  ? 

Because  some  sudden  change  of  temperature  has 
condensed  the  vapor  of  the  air  into  clouds. 

SO  8   Why  are  clouds  sometimes  dissipated  very  suddenly  ? 

Because  some  dry  wind  (blowing  over  the  clouds) 
imbibes  their  moisture,  and  carries  it  off  in  invisible 
vapor. 

0 O9  Why  does  wind  sometimes  Iring  rain,  and  sometimes  fine  weather  f 

If  the  wind  be  colder  than  the  clouds,  it  will  condense 
their  vapor  into  rain  /  but  if  the  wind  is  warmer  than 
the  clouds,  it  will  dissolve  them  and  cause  them  to  dis- 
appear. 

510  What  is  a  hurricane  f 

The  hurricane  is  a  remarkable  storm  wind,  peculiar 
to  certain  portions  of  the  world.  It  rarely  takes  its 
rise  beyond  the  tropics,  and  it  is  the  only  storm  to 
dread  within  the  region  of  the  trade-winds. 

511  How  are  hurricanes  especially  distinguished  from  other  kinds  of 
tempests  f 

By  their  extent,  irresistible  power,  and  the  sudden 
changes  that  occur  in  the  direction  of  the  wind. 

S1J3  Do  any  particular  portions  of  the  tropics  appear  to  be  especially 
visited  with  hurricanes  ? 

In  the  northern  hemisphere,  the  hurricane  most  fre- 
quently occurs  in  the  regions  of  the  West  Indies  ;  in 


SCIENCE   OF   COMMON   THINGS.  81 

What  are  hurricanes  ?  Breadth  and  velocity  of  hurricanes. 

the  southern  hemisphere,  it  occurs  in.  the  neighborhood 
of  the  Mauritius. 

513  Do  the  hurricanes  occur  at  particular  seasons  f 

The  West  Indian  occur  from  August  to  October  /  the 
Mauritian  from  February  to  April. 

514  What  have  recent  investigations  shown  the  hurricanes  to  be? 

Extensive  storms  of  wind,  which  revolve  round  an 
axis  either  upright  •  or  inclined  to  the  horizon ;  while 
at  the  same  time  the  body  of  the  storm  has  a  progres- 
sive motion  over  the  surface  of  the  ocean. 

515  Illustrate  more  clearly  the  manner  in  which  a  hurricane  moves  f 
It  is  the  nature  of  a  hurricane  to  travel  round  and 

round  as  well  as  forward,  much  as  a  corkscrew  tra- 
vels through  a  cork,  only  the  circles  are  all^^,  and  de- 
scribed by  a  rotatory  wind  upon  the  surface  of  the  water. 

516  In  ivhat  direction  would  a  ship  revolving  in  the  circles  of  a  hurri- 
cane find  the  wind  ? 

As  the  ship  revolved,  she  wrould  in  turn  find  the 
wind  blowing  from  every  point  of  the  compass. 

517  What  is  known  concerning  the  distance  travelled  by  hurricanes  f 

The  distance  traversed  by  these  terrible  tempests  is 
immense.  The  great  gale  of  August,  1830,  which  oc- 
curred at  St.  Thomas  on  the  12th,  reached  the  Banks 
of  Newfoundland  on  the  19th,  having  travelled  more 
than  three  thousand  nautical  miles  in  seven  days  /  the 
track  of  the  Cuba  hurricane  of  1844:  was  but  little  infe- 
rior in  length. 

518  What  is  known  of  their  progressive  and  rotary  velocity  f 

Their  progressive  velocity  is  from  seventeen  to  forty 
miles  per  hour  •  but  distinct  from  the  progressive  velo- 
city is  the  rotary,  which  increases  from  the  exterior 
boundary  to  the  centre  of  the  storm,  near  which  point 
the  force  of  the  tempest  is  greatest,  the  wind  sometimes 
blowing  at  the  rate  of  one  hundred  miles  per  hour. 

519  How  great  is  the  breadth  of  the  hurricane  $ 

The  surface  simultaneously  swept  by  these  tremen- 
dous whirlwinds  is  a  vast  circle  varying  from  one  hun- 
dred to  Jive  hundred  miles  in  diameter. 


82  SCIENCE   OF    COMMON   THINGS. 

Tornadoes-~cause  of.  Eddies  in  water. 

520  How  great  is  the  surface  over  whicJi  they  prevail  ? 

Mr.  Redfield,  of  New  York,  lias  estimated  the  great 
Cuba  hurricane  of  1844  to  have  been  not  less  than 
eight  hundred  miles  in  breadth,  and  the  area  over 
which  it  prevailed  during  its  whole  length  was  com- 
puted to  be  two  million  four  hundred  thousand  square 
'miles — an  extent  of  surface  equal  to  two-thirds  of  that 
of  all  Europe. 

521  What  curious  fact  have  mariners  noticed  when  in  the  centre  or 
vortex  of  the  hurricane  ? 

An  awful  calm  prevails,  described  as  the  lull  of  the 
tempest,  in  which  it  seems  to  have  rested  only  to 
gather  strength  for  greater  efforts. 

522  In  what  respect  does  a  tornado  differ  from  a  hurricane  f 

Tornadoes  may  be  regarded  as  hurricanes,  differing 
chiefly  in  respect  to  their  continuance  and  extent. 

523  How  long  do  they  usually  last  f 

From  fifteen  to  seventy  seconds. 

524  What  is  their  extent  f 

Their  breadth  varies  from  &few  rods  to  several  hun- 
dred yards,  and  the  length  of  their  course  rarely  ex- 
ceeds twenty  miles. 

525  What  phenomena  generally  attend  them  f 

The  tornado  is  generally  preceded  by  a  calm  and 
sultry  state  of  the  atmosphere,  when  suddenly  the 
whirlwind  appears,  prostrating  everything  before  it. 
Tornadoes  are  usually  accompanied  with  thunder  and 
lightning,  and  sometimes  showers  of  hail. 

526  What  is  supposed  to  be  the  origin  of  tornadoes  f 

They  are  supposed  to  be  generally  produced  by  the 
lateral  action  of  an  opposing  wind,  or  the  influence  of 
a  brisk  gale  upon  a  portion  of  the  atmosphere  in  repose. 

527  How  are  the  eddies  or  whirlpools  produced  which  occur  in  water, 
and  which  in  their  formation  resemble  some  tornadoes  f 

Eddies  or  whirlpools  are  most  frequently  formed  in 
water  when  two  streams  flowing  unequally  meet,  They 
may  be  seen  at  the  junction  of  two  brooks  or  rivers. 


SCIENCE   OF   COMMON   THINGS.  83 

Waterspouts.  Why  winds  feel  cool.  What  are  clouds? 

535  How  are  the  whirlwinds  which  we  frequently  see  at  the  corners  of 
streets  in  cities  produced  f 

They  are  caused  by  a  gust  of  wind  sweeping  round 
a  corner  of  a  building,  and  striking  the  calm  air  be- 
yond it. 

530   What  is  a  waterspout  f 

A  waterspout  is  a  whirlwind  over  the  surface  of 
water,  and  differs  from  a  whirlwind  on  land  in  the  fact 
that  water  is  subjected  to  the  action  of  the  wind,  instead 
of  objects  on  the  surface  of  the  earth. 

530  Why  does  wind  generally  feel  cold  f 

Because  a  constantly-changing  surface  comes  in  con- 
tact with  our  body  to  draw  off  its  heat. 

531  What  are  the  effects  of  wind  noticed  in  the  Arctic  regions  f 

Arctic  explorers  inform  us  that  in  those  regions,  when 
the  thermometer  ranges  from  40°  to  60°  below  zero, 
the  cold  of  the  external  air  is  easily  endurable,  provided 
the  air  is  calm  and  the  individual  exercises  freely  /  but 
if  a  wind  arises  at  this  temperature,  the  severity  of  the 
cold  becomes  too  great  for  human  endurance. 

533  If  the  winds  should  cease  to  blow  over  the  ocean,  what  would  be  the 
e/ectf 

The  water  would  undoubtedly  become  stagnant. 
Tempests  and  hurricanes  also  exercise  a  beneficial  effect 
by  agitating  and  purifying  the  atmosphere,  and  sweep- 
ing from  it  the  seeds  of  pestilence  and  contagion. 

533  What  are  clouds  f 

Moisture  evaporated  from  the  earth^  and  again  par- 
tially condensed  in  the  upper  regions  of  the  air. 

534  What  is  the  difference  between  a  fog  and  a  cloud  ? 

Clouds  and  fogs  differ  only  in  one  respect.  Clouds 
are  elevated  above  our  heads,  but  fogs  come  in  contact 
with  the  surface  of  the  earth. 

635    Why  are  clouds  higher  on  a  fine  day  f 

Because  they  are  lighter  and  more  buoyant. 

536  Why  are  clouds  lighter  on  a  fine  day  f 

1.  Because  the  vapor  of  the  clouds  is  less  condensed; 
and 


84:  SCIENCE   OF   COMMON  THINGS. 

Why  clouds  float  in  the  air.  Height  of  clouds.  Size  of  clouds. 

2.  The  air  itself  (on  a  fine  day)  retains  much  of  its 
vapor  in  an  invisible  form. 

537*   Why  do  clouds  float  so  readily  in  the  air  f 

Because  they  are  composed  of  very  minute  globules 
(called  vesicles),  which  (being  lighter  than  air)  float 
like  soap-bubbles. 

538  Are  att  clouds  alike  f 

No  ;  they  vary  greatly  in  density,  height,  and  color. 

530    What  is  the  chief  cause  of  fog  and  clouds  f 

During  the  daily  process  of  evaporation  from  the 
surface  of  the  earth,  warm,  humid  currents  of  air  are 
continually  ascending ;  the  higher  they  ascend,  the 
colder  is  the  atmosphere  into  which  they  enter  ;  and,  as 
they  continue  to  rise,  a  point  will  at  length  be  attained 
where,  in  union  with  the  colder  air,  their  original 
humidity  can  no  longer  be  retained  :  a  cloud  will  then 
appear,  which  increases  in  bulk  with  the  upward  pro- 
gress of  the  current  into  colder  regions. 

540  How  do  changes  in  the  wind  produce  clouds  f 

If  a  cold  current  of  wind  blows  suddenly  over  any 
region,  it  condenses  the  invisible  vapor  of  the  air  into 
cloud  or  rain  j  but  if  a  warm  current  of  wind  blows 
over  any  region,  it  disperses  the  clouds  by  absorbing 
their  vapor. 

541  What  distance  are  the  clouds  from  the  earth  f 

Some  thin,  light  clouds  are  elevated  above  the  high- 
est mountain-top  ;  some  heavy  ones  touch  the  steeples, 
trees,  and  even  the  earth  ;  but  the  average  height  ia 
between  one  and  two  miles. 

Streaky,  curling  clouds,  like  hair,  are  often  five  or  six  miles  high. 

542  What  is  the  size  of  the  clouds  f 

Some  clouds  are  many  square  miles  in  surface,  and 
above  a  mile  in  thickness  /  while  others  are  only  a  few 
yards  or  inches. 

543  How  can  persons  ascertain  the  thickness  of  a  cloud  f 

As  the  tops  of  high  mountains  are  generally  above 
the  clouds,  travellers  may  pass  quite  through  them  into 


SCIENCE   OF   COMMON   THINGS.  85 

Cause  of  the  appearance  of  clouds.  Color  of  clouds. 

a  clear  blue  firmament,  when  the  clouds  will  be  seen 
beneath  their  feet. 

544  Why  do  clouds,  when  not  continuous  over  the  whole  surface  of  the 
sky,  appear  jagged,  rough,  and  uneven  ? 

The  rays  of  the  sun,  falling  upon  different  surfaces  at 
different  angles,  melt  away  one  set  of  elevations,  and 
create  another  set  of  depressions  ;  the  heat  also  which  is 
liberated  from  below  in  the  process  of  condensation, 
the  currents  of  warm  air  escaping  from  the  earth,  and 
of  cold  air  descending  from  above,  all  tend  to  keep  the 
clouds  in  a  state  of  agitation,  upheaval,  and  depression. 
Under  their  various  influences  the  masses  of  vapor 
composing  the  clouds  are  caused  to  assume  all  manner 
of  grotesque  and  fanciful  shapes. 

545  What  effect  have  winds  on  the  shape  of  clouds  f 

They  sometimes  absorb  them  entirely ;  sometimes 
increase  their  volume  and  density  ;  and  sometimes 
change  the  position  of  their  parts. 

546  How  can  winds  absorb  clouds  altogether  ? 

Warm,  dry  winds  will  convert  the  substance  of  clouds 
into  invisible  vapor,  which  they  will  carry  away  in 
their  own  current. 

54*7  How  can  winds  increase  the  bulk  and  density  of  clouds  f 

Cold  currents  of  wind  wrill  condense  the  invisible 
vapor  of  the  air,  and  add  it  to  the  clouds  with  which, 
they  come  in  contact. 

54S    Why  is  not  the  color  of  clouds  always  alike  f 

Because  their  size,  density,  and  situation  in  regard  to 
the  sun  are  perpetually  varying,  so  that  sometimes  one 
color  is  reflected  and  sometimes  another. 

549  Why  do  the  clouds  after  sunset  about  the  western  horizon  often 
exhibit  a  beautiful  crimson  appearance  ? 

Because  the  red  rays,  of  which  the  sun's  light  is  in 
part  composed,  are  less  refrangible  than  any  of  the 
other  colors.  In  consequence  of  this,  they  are  not  bent 
out  of  their  course  so  much  as  the  blue  and  yellow  rays, 
and  are  the  last  to  disappear. 

For  the  same  reason  they  are  the  first  to  appear  in 


86  SCIENCE   OF   COMMON"  THINGS. 


Eeft  uigibility  of  light  Red  clouds  at  sunrise  and  sunset. 

the  morning  when  the  sun  rises,  and  impart  to  the 
morning  clouds  red  or  crimson  colors. 


Fig.  19. 

Let  us  suppose,  as  in^.  19,  a  ray  oflight,  proceeding  from  the  sun,  S, 
to  enter  the  earth's  atmosphere  at  the  point  P.  The  red  rays,  which 
compose  in  part  the  solar  beam,  being  the  least  refrangible,  or  the  least 
deviated  from  their  course,  will  reach  the  eye  of  a  spectator  at  the  point 
A ;  while  the  yellow  and  blue  rays,  being  refracted  to  a  greater  degree, 
will  reach  the  surface  of  the  earth  at  the  intermediate  points  B  and  C. 
They  will,  consequently,  be  quite  invisible  from  the  point  A. 

550  What,  is  meant  by  being  "  less  refrongiblef'1 

Being  less  able  to  be  bent.  Blue  and  yellow  rays  are 
more  easily  bent  below  the  horizon  through  the  action 
of  the  atmosphere,  but  red  rays  are  not  so  much  bent 
down,  and  therefore  we  see  them  later  in  the  evening. 

551  What  is  the  cause  of  a  red  sunset  f 

The  vapor  of  the  air  not  being  actually  condensed 
into  clouds,  but  only  on  ihe  point  of  being  condensed. 

In  the  same  manner,  if  light  be  transmitted  through  steam  mingled 
with  air,  and  therefore  on  the  verge  of  condensation,  it  assumes  a  deep 
orange  or  red  color. 

552  Why  is  a  red  and  lowering  sky  at  sunrise  an  indication  of  a  wet 
day  f 

The  red  and  lowering  appearance  of  the  morning  sky? 
which  indicates  foul  weather,  probably  depends  upon 
such  an  excess  of  vapor  being  present  in  the  whole 
atmosphere  that  clouds  are  actually  forming  in  the 


SCIENCE    OF   COMMON   THINGS.  87 

Haziness  of  the  Indian  summer.  When  vapor  forms  clouds  and  fogs. 

higher  regions,  or  upon  the  point  of  condensation,  which 
the  rising  sun  cannot  disperse. 

Hence  our  Lord's  observation — "  In  the  morning  ye  say,  It  will  be  foui 
weather  to-day,  for  the  sky  is  red  and  lowering."  (Matt.  xvi.  3.) 

553  Which  is  the  most  transparent,  dry  or  moist  air  ? 

Air  moderately  moist  is  more  transparent  than  very 
dry  air. 

554  What  is  the  cause  of  the  haziness  of  the  atmosphere  during  that 
portion  of  the  autumn  known  as  the  "  Indian  Summer  f  " 

It  is  undoubtedly  due  to  several  causes  ;  partially  to 
an  excessive  dryness  of  the  atmosphere,  and,  in  some 
degree,  to  the  prevalence  of  smoke  in  the  air  arising 
from  burning  forests.  But  it  is  also  a  fact,  ascertained 
within  a  few  years,  that  the  constitution  of  the  atmo- 
sphere is  changed  in  the  autumn,  and  that  solar  light 
at  that  season  has  less  chemical  influence  than  at  any 
other  portion  of  the  year. 

555  Why  does  the  sun  seen  through  a  fog  appear  red? 

Because  the  red  rays  of  light  have  a  greater  power  to 
pass  through  a  thick,  dense  atmosphere  than  any  of  the 
other  colored  rays. 

556  Why  does  vapor  sometimes  form  into  clouds,  and  sometimes  rest 
upon  the  earth  as  mist  or  fog? 

This  depends  on  the  temperature  of  the  air.  "When 
the  surface  of  the  earth  is  warmer  than  the  lower  air, 
the  vapor  of  the  earth  (being  condensed  by  the  chill 
air)  becomes  mist  or  fog.  But  when  the  lower  air  is 
warmer  than  the  earth,  the  vapor  rises  through  the  air, 
and  becomes  cloud. 

557*  Why  do  clouds  often  hover  around  mountain  peaks,  when  the 
atmosphere  elsewhere  is  clear  and  free  from  clouds  1 

It  is  caused  by  the  wind  impelling  up  the  sides  of 
the  mountains  the  warm  humid  air  of  the  valleys, 
which  in  its  ascent  gradually  becomes  condensed  by 
the  cold,  and  its  excess  of  moisture  becomes  visible, 
and  appears  as  a  cloud. 

558  Why  are  windoios  at  night  often  covered  with  thick  mist,  and  the 
frames  wet  with  standing  water  ? 

Because  the  temperature  of  the  external  air  always 


88  SCIENCE   OF   COMMON   THINGS. 

Mist  on  windows.  Insensible  perspiration. 


falls  at  sunset,  and  chills  the  window-glass  with  which 
it  comes  in  contact. 

559  How  does  this  account  for  the  mist  and  water  on  a  window  f 

As  the  warm  vapor  of  the  room  touches  the  cold 
glass  it  is  chilled  and  condensed  into  mist,  and  the  mist 
(collecting  into  drops)  rolls  down  the  window-frame  in 
little  streams  of  water. 

560  Does  the  glass  of  a  ivindow  cool  down  more  rapidly  than  the  air 
of  the  room  itself  f 

Yes  ;  because  the  air  is  kept  warm  by  fires  and  by 
the  animal  heat  of  the  people  in  the  room ;  in  conse- 
quence of  which  the  air  of  a  room  suffers  very  little 
diminution  of  heat  from  the  setting  of  the  sun. 

561  Whence  arises  the  vapor  of  a  room  f 

The  air  of  the  room  always  contains  vapor ;  vapor 
also  arises  from  the  breath  and  insensible  perspiration  of 
the  inmates,  from  cooking  and  the  evaporation  of  water. 

563   What  is  meant  by  "  the  insensible  perspiration  f " 

From  every  part  of  the  human  body  an  insensible 
and  invisible  perspiration  issues  all  night  and  day,  not 
only  in  the  hot  weather  of  summer,  but  also  in  the 
coldest  days  of  winter. 

563  If  the  perspiration  be  both  insensible  and  invisible,  hoiu  is  it  known 
that  there  is  any  such  perspiration  ? 

If  you  put  your  naked  arm  into  a  clean,  dry  glass 
tube,  the  perspiration  will  condense  on  the  glass  like 
mist. 

564  Why  is  a  tumbler  of  cold  water  made  quite  dull  with  mist,  when 
brought  into  a  warm  room  ? 

Because  the  hot  vapor  of  the  room  is  condensed  upon 
the  cold  tumbler,  with  which  it  comes  in  contact,  and 
changes  its  invisible  and  gaseous  form  into  that  of  dew. 

565  Why  does  breathing  on  a  glass  make  it  quite  dull  f 

Because  the  cold  glass  condenses  the  invisible  vapor 
contained  in  warm  breath,  and  converts  it  into  dew. 

566  Why  are  the  walls  of  a  house  covered  with  damp  in  a  sudden 
thaw? 

Because  the  walls  (being  thick)  cannot  change  their 


SCIENCE   OF   COMMON   THINGS.  89 


Breath  visible  in  cold  weather.  Difference  between  mist  and  fog. 

temperature  as  fast  as  the  air  ;  in  consequence  of  which 
they  retain  their  cold  after  the  thaw  lias  set  in. 

567  How  does  "retaining  their  cold"  account  for  their  being  so  wet? 

As  the  vapor  of  the  warm  air  touches  the  cold  walls, 
it  is  chilled  and  condensed  into  water,  which  either 
sticks  to  the  walls  or  trickles  down  in  little  streams. 

568  Why  is  our  breath  visible  in  winter,  and  not  in  summer  ? 

Because  the  intense  cold  condenses  its  moisture  into 
visible  vapor,  but  in  summer  the  air  is  not  cold  enough 
to  do  so. 

569  Why  are  our  hair  and  the  brim  of  our  hat  often  covered  with  lit- 
tle drops  of  pearly  dew  in  ivinter-time  f 

Because  the  vapor  of  the  breath  condenses  as  it  comes 
in  contact  with  our  cold  hair  or  hat,  and  hangs  there 
in  little  dew-drops. 

570  What  are  fogs  f 

Fogs  are  visible  vapors  that  float  in  the  atmosphere 
near  the  surface  of  the  earth. 

571  What  is  the  cause  of  fogs  1 

They  originate  in  the  same  causes  as  rain — the  union 
of  a  cool  body  of  air  with  one  that  is  warm  and  humid  ; 
when  the  precipitation  of  moisture  is  slight,  fogs  are 
produced  ;  when  it  is  copious,  rains  are  the  result. 

573    What  distinction  is  to  be  made  between  a  mist  and  a  fog  ? 

Mist  is  generally  considered  to  be  a  fine  rain,  while 
fog  is  vapor  not  sufficiently  condensed  to  allow  of  its 
precipitation  in  drops. 

The  term  mist  is  also  generally  applied  to  vapors  condensed  on  marshes, 
rivers,  and  lakes,  while  the  name  fog  is  often  applied  to  vapors  condensed 
on  land,  especially  if  those  vapors  are  laden  with  smoke. 

573  Why  does  not  the  fog  become  dew  ? 

Because  the  chill  of  the  air  is  so  rapid  that  vapor  is 
condensed  faster  than  it  can  be  deposited,  and  covering 
the  earth  in  a  fog)  prevents  any  further  radiation  of 
heat  from  the  earth. 

574  When  the  earth  can  no  longer  radiate  heat  upwards,  does  it  con- 
tinue to  condense  the  vapor  of  the  air  ? 

Ko ;  the  air  (in  contact  with  the  earth)  becomes 


90  SCIENCE   OF  COMMON   THINGS. 

When  fogs  occur.  When  vapor  forms  clouds  and  when  fogs. 

about  equal  in  temperature  with  the  surface  of  the 
earth  itself;  for  which  reason  the  fog  is  not  condensed 
into  dew,  but  remains  floating  above  the  earth  as  a 
thick  cloud. 

57*5  This  fog  seems  to  rise  higher  and  higher,  and  yet  remains  quite  as 
dense  below  as  at  first :  explain  the  cause  of  this  ? 

The  air  resting  on  the  earth  is  first  chilled,  and  chills 
the  air  resting  on  it ;  the  air  which  touches  this  new 
layer  of  fog  being  also  condensed,  layer  is  added'  to, 
layer ;  and  thus  the  fog  seems  to  be  rising,  when  (in 
fact)  it  is  only  deepening. 

57*B    Why  are  there  not  fogs  every  night  f 

Because  the  air  will  always  hold  in  solution  a  cer- 
tain quantity  of  vapor  (which  varies  according  to  its 
temperature) ;  and,  when  the  air  is  not  saturated,  it 
may  be  cooled  without  parting  with  its  vapor. 

57"?   Wften  do  fogs  occur  at  night  f 

When  the  air  is  saturated  with  vapor  during  the 
day.  When  this  is  the  case,  it  deposits  some  of  its 
superabundant  moisture  in  the  form  of  dew  or  fog  as 
soon  as  its  capacity  for  holding  vapor  is  lessened  by 
the  cold  night. 

578  Why  is  there  very  often  a  fog  over  marshes  and  rivers  at  night- 
time ? 

Because  the  air  of  marshes  is  almost  always  near 
saturation •  and  therefore  the  least  depression  of  tem- 
perature will  compel  it  to  relinquish  some  of  its  moist- 
ure in  the  form  of  dew  or  fog. 

57*9  Why  does  vapor  sometimes  form  into  clouds,  and  sometimes  rest 
upon  the  earth  as  mist  or  fog  1 

This  depends  on  the  temperature  of  the  air.  "When 
the  surface  of  the  earth  is  warmer  than  the  air,  the 
vapor  of  the  earth  (being  condensed  by  the  chill  air) 
becomes  mist  or  fog.  But,  when  the  air  is  warmer 
than  the  earth,  the  vapor  rises  through  the  air,  and  be- 
comes cloud. 

58O  If  cold  air  produces  fog,  why  is  it  not  foggy  on  a  frosty  morning  f 

1,  Because  less  vapor  is  formed  on  a,  frosty  day ; 


SCIENCE   OF   COMMON   THINGS.  91 

What  is  rain  ?  Why  falls  in  drops. 

and  2.  The  vapor  is  frozen  upon  the  ground  before  it 
ean  rise  from  the  earth,  and  becomes  hoar-frost. 

581    What  is  rain? 

Rain  is  the  vapor  of  the  clouds  or  air  condensed  and 
precipitated  to  the  earth. 

58J3  In  what  manner  is  the  vapor  of  the  air  condensed  so  as  to  form 
rain  ? 

i  When  two  or  more  volumes  of  humid  air  differing 
considerably  in  temperature  unite,  the  several  portions 
in  union  are  incapable  of  absorbing  the  same  amount 
of  moisture  that  each  could  retain  if  they  had  not 
united.  The  excess  of  moisture,  if  very  great,  is  pre- 
cipitated as  rain  ;  if  in  slight  amount,  it  appears  as 
clouds,  fogs,  or  mists. 

583  Upon  what  law  does  this  condensation  of  vapor  and  formation  of 
rain  depend  f 

Upon  the  law  that  the  capacity  of  the  air  for  moist- 
ure decreases  in  a  greater  ratio  than  the  temperature. 

58*4    Why  does  rainfall  in  drops  ? 

Because  the  vapory  particles  in  their  descent  attract 
each  other  ;  and  those  which  are  sufficiently  near  unite 
and  form  into  drops. 

The  size  of  the  rain-drop  is  increased  according  to  the  rapidity  with 
which  the  vapors  are  condensed. 

585    Why  does  not  the  cold  of  night  always  cause  ram  f 

Because  the  air  is  not  always  near  saturation  ;  and 
unless  this  be  the  case,  it  will  be  able  to  hold  its  vapor 
in  solution,  even  after  it  is  condensed  by  the  chilly 
night. 

580    Why  does  a  passing  cloud  often  drop  rain  ? 

Because  the  cloud  (travelling  about  on  the  wind) 
comes  into  contact  with  something  that  chills  it; 
and  its  vapor  being  condensed,  falls  to  the  earth  as 


58  T  Can  the  air  absorb  moisture  at  all  temperatures,  and  retain  it  in 
an  invisible  state  f 

It  can  ;   and  this  power  of  the  air  is  termed  its 
capacity  of  absorption. 


92  SCIENCE   OF  COMMON  THINGS. 

What  is  snow  ?  Cause  of  sleet. 

588  How  much  moisture  can  a  volume  of  air  at  32°  F.  absorb  f 

An  amount  equal  to  the  hundred  and  sixtieth  part 
of  its  own  weight. 

589  How  does  the  capacity  of  air  for  moisture  increase  with  the  tem- 
perature ? 

Eor  every  27  additional  degrees  of  heat,  the  quantity 
of  moisture  it  can  absorb  at  32°  is  doubled.  Thus  a 
body  of  air  at  32°  F.  absorbs  the  160th  part  of  its  own 
weight;  at  59°  F.  the  80th;  at  86°  F.  the  40th;  at 
113°  F.  the  20th  part  of  its  own  moisture.  It  follows 
from  this  that,  while  the  temperature  advances  in  an 
arithmetical  series,  the  capacity  is  accelerated  in  geo- 
metrical series.  , 

590  In  what  situations  is  the  air  always  saturated  f 

Over  the  ocean  and  upon  the  adjacent  coasts. 

591  Where  is  the  absolute  humidity  of  the  atmosphere  the  greatest  f 

In  the  tropics,  where  the  temperature  of  the  air,  and 
its  consequent  capacity  for  moisture,  is  the  greatest. 

593   What  is  snow  ? 

The  condensed  vapor  of  the  air  frozen  and  precipi- 
tated to  the  earth. 

593  What  is  the  cause  of  snow  f 

When  the  air  is  nearly  saturated  with  vapor,  and 
is  acted  on  by  a  current  of  air  l>elow  the  freezing  point, 
some  of  the  vapor  is  condensed,  and  frozen  into  snow. 

A  few  years  ago,  some  fishermen  (who  wintered  at  Nova  Zembla), 
after  they  had  been  shut  up  in  a  hut  for  several  days,  opened  the  window, 
and  the  cold  external  air  rushing  in,  instantly  condensed  the  air  of  the 
hut,  and  its  vapor  fell  on  the  floor  in  a  shower  of*now. 

594  What  is  the  cause  of  sleet  ? 

"When  flakes  of  snow  (in  their  descent)  pass  through 
a  bed  of  air  above  the  freezing  point,  they  partially 
melt,  and  fall  to  the  earth  as  half-melted  snow,  or 
sleet. 

595  How  does  snow  prove  beneficial  to  the  earth  in  the  cold  season  f 

It  keeps  the  surface  of  the  earth  warm,  protects  vege- 
tation to  a  considerable  extent  from  the  cold,  and  acts 
as  a  fertilizer. 


SCIENCE    OF   COMMON   THINGS.  93 

How  snow  keeps  the  earth  warm.  Why  snow  is  white. 


596  Does  snow  Jceep  the  earth  warm  f 

Yes,  because  it  is  a  very  bad  conductor  j  in  conse- 
quence of  which,  when  the  earth  is  covered  with  snow, 
its  temperature  very  rarely  descends  below  the  freezing 
point,  even  when  the  air  is  fifteen  or  twenty  degrees 
colder. 

59  7    Why  is  snow  a  lad  conductor  of  heat  and  cold  f 

Because  air  is  confined  among  the  crystals,  and  air 
is  a  very  bad  conductor ;  when,  therefore,  the  earth  is 
covered  with  snow,  it  cannot  throw  off  its  heat  by 
radiation. 


Why  is  there  no  snow  in  summer-time  f 

Because  the  heat  of  the  air  adjacent  to  the  earth 
melts  it  in  its  descent,  and  prevents  it  from  reaching 
the  surface  of  the  earth. 

590    Why  is  snow  white  f 

Because  it  is  formed  of  an  infinite  number  of  very 
minute  crystals  and  prisms,  which  reflect  all  the  colors 
of  the  ravs  of  light  from  different  points,  and  these 
colors,  uniting  before  they  meet  the  eye,  cause  snow  to 
appear  white. 

The  same  answer  applies  to  salt,  loaf-sugar,  etc. 

GOO  Under  what  circumstances  does  snow  fall  in  large  flakes,  and  when 
in  small  f 

The  largest  flakes  are  formed  when  the  air  abounds 
with  vapor,  and  the  temperature  is  about  32°  F. ;  but 
as  the  moisture  diminishes,  and  the  cold  increases,  the 
snow  becomes  finer. 

6O1    What  is  the  snow  flake  composed  off 

Regular  and  symmetrical  crystals,  having  a  great 
diversity  of  forms. 

6  OS  Do  we  see  the  same  crystals  in  ice  f 

They  exist  in  ice,  but  are  so  blended  together  that 
their  symmetry  is  lost  in  the  compact  mass. 

6O3  How  much  more  bulky  is  snow  than  water  ? 

The  bulk  of  recently-fallen  snow  is  ten  or  twelve  times 
greater  than  that  of  the  water  obtained  by  melting  it 

fi 


94:  SCIENCE   OF   COMMON   THINGS. 

Red  and  green  snow.  "What  is  hail  ?  Meteorites. 

GO4  Does  snow  ever  occur  of  any  other  appearance  than  white? 

Yes ;  in  the  Arctic  regions  and  on  some  mountains 
it  is  red,  and  occasionally  green. 

6O5   What  is  the  cause  of  these  appearances  1 

These  singular  hues  are  occasioned  by  little  micro- 
scopic plants,  which  germinate  and  live  in  the  snow. 
They  consist  of  little  globules  from  TTfTo-  of  an  inch  to 
3-500  °f  an  inch.  Each  globule  is  divided  into  seven 
or  eight  cells  filled  with  a  liquid,  which  gives  a  color 
to  the  snow,  and  is  sometimes  green  and  sometimes  red. 

eoe    What  is 'hail? 

Rain,  which  has  passed  in  its  descent  through  some 
cold  bed  of  air,  and  has  been  frozen  into  drops  of  ice. 

GOT*   What  makes  one  bed  of  air  colder  than  another  f 

It  is  frequently  caused  by  electricity  unequally  dis- 
tributed in  the  air. 

60S  How  can  electricity  make  air  cold  ? 

Air,  when  electrified,  is  expanded,  and  expansion 
produces  cold. 

6O9    Why  does  hail  fall  generally  in  summer  and  autumn  f 

Because  the  air  is  more  highly  electrified  in  summer 
and  autumn  than  in  winter  and- spring;  and  the  vapors 
in  summer  and  autumn  (being  rarefied)  ascend  to  more 
elevated  regions,  which  are  colder  than  those  nearer 
the  earth. 

G1O  Is  the  occurrence  and  formation  of  hail  clearly  understood? 

It  is  not ;  much  information  exists  upon  the  subject, 
but  no  theory  has  yet  been  formed  which  satisfactorily 
accounts  for  all  the  facts  which  have  been  observed. 

Gil   What  are  meteorites  f 

Meteorites  are  solid,  luminous  bodies,  which  from 
time  to  time  visit  the  earth,  moving  with  immense 
velocity,  and  remaining  visible  but  for  a  few  moments. 
They  are  generally  accompanied  by  a  luminous  train, 
and  during  their  progress  explosions  are  often  heard. 

61Q   What  is  an  aerolite  f 

The  term  aerolite  is  given  to  those  stony  masses  of 


SCIENCE   OF   COMMON   THINGS.  95 

Aerolites.  Appearance.  Composition. 

matter  which   are   sometimes   seen   to   fall  from  the 
atmosphere. 

It  is  derived  from  the  Greek  words,  acp  (atmosphere),  and  Xi0<>?  (a  stone). 
A  meteor  is  distinguished  from  an  aerolite  by  the  fact  that  it  bursts  in 
the  atmosphere,  but  leaves  no  residuum  except  a  vapor-like  smoke ; 
while  the  aerolite,  which  is  supposed  to  be  a  fragment  of  a  meteor,  comes 
to  the  ground. 

613  What  is  the  weight  of  those  aerolites  which  have  been  known  to  fall 
from  the  atmosphere  ? 

Their  weights  vary  from  a  few  ounces  to  several  hun- 
dred pounds,  or  even  tons. 

614  At  what  height    in   the  atmosphere  are    meteors    supposed  to 

appear f 

Their  height  above  the  earth  has  been  estimated  to 
vary  from  eighteen  to  eighty  miles. 

615  With  what  velocity  do  they  move  ? 

The  velocity  of  these  bodies  is  somewhat  more  than 
three  hundred  miles  per  minute,  though  one  meteor  of 
immense  size,  wrhich  is  supposed  to  have  passed  within 
twenty-five  miles  of  the  earth,  moved  at  the  rate  of 
twelve  hundred  miles  per  minute. 

616  What  is  the  value  of  such  estimates  ? 

Owing  to  the  short  time  the  meteor  is  visible  and  its 
great  velocity,  accurate  observations  cannot  be  made 
upon  it ;  and  all  estimates  respecting  their  distance, 
size,  etc.,  must  be  considered  as  only  approximations 
to  the  truth. 

617  What  is  the  general  appearance  of  aerolites  f 

Most  of  them  are  covered  with  a  Hack  shining  crust, 
as  if  the  body  had  been  coated  with  pitch.  When 
broken  their  color  is  ash-grey,  inclining  to  black. 

Very  many  of  the  meteorites  which  have  fallen  at  different  times  and 
m  different  parts  of  the  globe,  resemble  eacli  other  so  closely,  that  they 
would  seem  to  have  been  broken  from  the  same  piece  or  mass  of  matter. 

618  What  is  their  composition  ? 

Great  numbers  of  aerolites  have  been  analysed,  and 
found  to  contain  nineteen  or  twenty  different  elementary 
substances.  But  for  the  most  part  they  consist  of  malle- 
able iron  and  niokel. 


96  SCIENCE    OF   COMMON   THINGS. 

Meteoric  iron.  Origin  of  meteors.  Shooting  stars. 

619  Do  tJie  aerolites  resemUe  in  composition  any  other  bodies  upon  the 
surface  of  the  earth  f 

They  do  not :  malleable  iron  is  rarely  if  ever  found 
in  terrestrial  substances  /  and  metallic  nickel  does  not 
occur  upon  the  surface  of  the  earth  naturally. 

620  What  is  peculiar  to  the  composition  of  meteoric  iron  t 

It  has  a  highly  crystalline  arrangement,  so  peculiar 
that  it  is  especially  distinguished  by  it.  This  arrange- 
ment .of  its  particles  enables  us  to  decide  upon  the 
meteoric  origin  of  masses  of  iron  which  are  occasionally 
found  scattered  up  and  down  the  surface  of  the  earth. 

621  Where  have  such  masses  been  found? 

In  the  south  of  Africa,  in  Mexico,  /Siberia,  and  on 
the  route  overland  to  California.  Some  of  these  masses 
are  of  immense  weight,  and  undoubtedly  fell  from  the 
atmosphere. 

622  How  are  meteorites  supposed  to  originate  ? 

four  hypotheses  have  been  advanced  to  account  for 
the  origin  of  these  extraordinary  bodies  :  1.  That  they 
are  thrown  up  from  terrestrial  volcanoes.  2.  That  they 
are  produced  in  the  atmosphere  from  vapors  and  gases 
exhaled  from  the  earth.  3.  That  they  are  thrown  from 
lunar  volcanoes.  4.  That  they  are  of  the  same  nature 
as  the  planets,  either  derived  from  them,  or  existing 
independently. 

623  Which  of  these  hypotheses  is  regarded  as  most  probabk  ? 

The  fourth  most  fully  explains  the  facts  connected 
with  the  appearance  of  meteorites,  and  the  third  like- 
wise has  some  strong  evidence  in  its  favor. 

624  In  what  respect  do  shooting  stars  differ  from  meteors  ? 

Their  altitude  and  velocity  are  greater,  they  are  far 
more  numerous  and  frequent,  and  are  unaccompanied 
by  any  sound  or  explosion.  Their  brilliancy  is  also 
much  inferior  to  that  of  the  meteor  /  and  no  portion  of 
their  substance  is  ever  known  to  have  reached  the  earth. 

625  What  do  we  know  concerning  their  altitude  f 

Owing  to  their  great  number  and  frequency  of  occur- 
rence, many  careful  observations  have  been  made  upon 


SCIENCE   OF   COMMON   THINGS.  97 


Origin  of  shooting  stars.  Zodiacal  light. 


them  ;  their  altitude  is  supposed  to  vary  from  six  to 
four  hundred  and  sixty  miles,  the  greatest  number 
appearing  at  a  height  of  about  seventy  mites. 

636    What  is  their  supposed  velocity  ? 

It  is  supposed  to  range  from  sixty  to  fifteen  hundred 
miles  per  minute. 

637*  Are  meteors  and  shooting  stars  at  all  times  equally  abundant  f 

They  are  not  •  some  may  be  seen  every  clear  night, 
but  they  appear  to  return  at  certain  periodical  epochs, 
when  they  descend  literally  in  showers. 

638  What  are  the  periods  when  they  may  be  noticed  most  abundantly  f 

On  the  9tk  and  Wth  of  August,  and  the  12^A  and 
13t/t  of  November. 

They  have  also  been  noticed  in  unusual  abundance  on  the  18th  of  Octo- 
ber, the-  6th  and  7th  of  December,  the  2d  of  January,  the  23d  and  24th  of 
April,  and  from  the  18th  to  the  20th  of  June. 

639  Do  the  shooting  stars  appear  to  emanate  from  any  particular  part 
of  the  heavens  ? 

The  majority  seem  to  start  from  a  point  in  the  con- 
stellation Perseus,  and  undoubtedly  far  beyond  the 
limits  of  our  atmosphere. 

63O    What  is  the  zodiacal  light  f 

It  is  a  singular  luminous  appearance  seen  in  the 
horizon  before  sunrise  and  after  sunset,  most  conspicu- 
ously in  the  months  of  April  and  May. 

Observations  made  during  the  year  1855  seem  to  conclusively  prove 
that  the  appearance  known  as  the  "  zodiacal  light "  is  occasioned  by  a 
ring  of  nebulous  matter  encircling  and  pertaining  to  the  earth. 


CHAPTER   YII. 

THE    PUMP    AND    BAROMETER. 

631    Why,  when  we  suck  up  a  liquid  with  a  tube  or  straiv,  does  th& 
liquid  rise  to  the  mouth  1 

One  end  of  the  tube  being  placed  between  the  lips, 


SCIENCE   OF   COMMON  THINGS. 


The  common  pump. 


How  constructed. 


Pump  valves. 


the  air  is  removed  from  the  tube  by  the  ordinary  pro- 
cess of  inhaling,  when  the  pressure  of  the  atmosphere 
compels  the  liquid  to  fill  the  space  deserted  by  the  air. 

633  Through  how  great  a  length  of  tube  could  tve  raise  a  liquid  by 
suction  ? 

About  thirty-two  feet. 

633    Why  can  we  not  raise  it  above  thirty-two  feet  f 

Because  the  atmospheric  pressure  will  only  support 
or  balance  a  column  of  water  or  similar  liquid  of  that 
height. 

634  How  is  the  common  pump  constructed  ? 

The  common  pump  consists  of  a 
hollow  tube,  the  lower  part  of  which, 
descending  into  the  water,  is  called 
the  siiction-pipe,  and  the  upper  part,  b 
(Fig.  20),  the  barrel  or  cylinder  •  of  a 
spout,  s,  at  the  top  of  the  cylinder ;  of 
an  air-tight  piston,  which  works  up 
and  down  in  the  cylinder ;  and  of  two 
valves,  both  opening  upwards,  one  of 
which,  g,  is  placed  at  the  top  of  the 
suction-pipe,  and  the  other,  p,  in  the 
piston. 

635  How  does  the  common  pump  operate  f 

When  the  piston  is  raised  from  the 
bottom  of  the  cylinder,  the  air  above 
it  is  drawn  uj?,  leaving  a  vacuum  be- 
low the  piston  ;  the  water  in  the  well 
then  rushes  up  through  the  valve,  g, 
and  fills  the  cylinder  ;  the  piston  is  then  forced  down, 
shutting  the  valve,  g,  and  causing  the  water  to  rise 
through  the  piston-valve,  p  ;  the  piston  is  then  raised, 
closing  its  valve,  and  raising  the  water  above  it,  which 
flows  out  of  the  spout,  s. 

636    What  is  a  valve  f 

A  valve,  in  general,  is  a  contrivance  by  which  water 
or  other  fluid,  flowing  through  a  tube  or^  aperture,  is 
allowed  free  passage  in  one  direction,  but  is  stopped  in 


Fig.  20. 


SCIENCE   OF   COMMON   THINGS.  99 


Common  suction-pump.  Height  water  rises  in  common  pump. 

the  other.  Its  structure  is  such,  that,  while  the 
pressure  of  fluid  on  one  side  has  a  tendency  to  close 
it,  the  pressure  on  the  other  side  has  a  tendency  to 
open  it. 

/tys.  21,  22,  and  23  represent  the  various  forms  of  valves  used  in 
pumps,  water-engines,  etc. 


Fig.  at.  Fig.  22.  Fig.  53. 


637  How  can  water  be  raised  by  the  common  suction-pump  ? 

As  the  action  of  this  pump  depends  upon  the  pressure 
of  the  atmosphere,  water  cannot  be  raised  by  it  from  a 
depth  of  more  than  34  feet  below  the  upper  valve,  and 
in  practice  a  much  shorter  limit  is  usually  assigned. 

633  A  tinman  of  Seville,  in  Spain,  ignorant  of  the  principles  of  science, 
undertook  to  construct  a  suction-pump  to  raise  water  from  a  well  sixty  feet 
deep ;  when  the  machine  was  finished,  he  was  confounded  at  discovering 
that  it  had  no  power  to  raise  water  at  all,  and  enraged  at  his  disappoint- 
ment, while  some  one  was  working  the  pump,  he  struck  the  suction  pipe  with 
a  hammer  or  axe  so  forcibly  as  to  crack  it,  when,  to  his  surprise  and  delight, 
the  water  almost  immediately  began  to  flow,  and  he  found  he  had  attained 
his  purpose.  How  is  this  result  to  be  accounted  for  ? 

The  explanation  is  as  follows :  the  air  pressed  in 
through  the  slit,  or  aperture  of  the  suction-pipe,  and 
becoming  mixed  with  the  water  in  its  ascent,  formed  a 
compound  fluid  far  lighter  than  water  alone,  and  there- 
fore acted  upon  more  readily  by  the  atmospheric  pres- 
sure ;  and  thus  produced  the  phenomenon  described. 

639  How  high  can  water  be  raised  in  the  suction-pump  by  resorting  t* 
Hie  expedient  above  described  ? 

About  fifty-five  feet,  instead  of  thirty  to  thirty-four. 

6*1O   To  whom  is  the  invention  oftJie  common  pump  attributed  ? 

To  Ctesibius,  an  Athenian  engineer,  who  lived  at 
Alexandria,  in  Egypt,  about  the  middle  of  the  second 
century  before  the  Christian  era. 


100 


SCIENCE   OF   COMMON   THINGS. 


Forcing-pump. 


Construction  of  chain-pump. 


Fig.  24. 


641    When  it  is  desired  to  raise  ivater  above  thirty -four  feet,  as  in  fire- 
engines,  etc.,  how  is  it  accomplished  ? 

By  means  of  tliQ  forcing-pump. 

643  In  what  manner  is  the  forcing-pump  con- 
structed ? 

In  the  forcing-pump  atmospheric 
pressure  plays  but  a  small  part.  There 
is  no  valve  in  the  piston  c  (fig.  24), 
but  the  water  raised  through  the  suc- 
tion-pipe #,  and  the  valve  <?,  is  forced 
by  each  depression  of  the  piston  -up 
through  the  pipe  e  e,  which  is  furnished 
with  a  valve  to  prevent  the  return  of 
the  fluid. 

643   What  is  a  chain-pump  f 

The  chain-pump  consists 
of  a  tube  or  cylinder,  the 
lower  part  of  which  is  im- 
mersed in  a  well  or  reser- 
voir, and  the  upper  part 
enters  the  bottom  of  a  cistern 
into  which  the  water  is  to 
be  raised.  A  chain  is  carried 
round  a  wheel  at  the  top, 
and  is  furnished  at  equal 
distances  with  movable 
bottoms,  which  fit  water- 
tight in  the  tube.  As  the 
wheel  revolves,  they  succes- 
sively  enter  the  tube,  and 
carry  the  water  up  before 
|  them,  which  is  discharged 
into  the  cistern  at  the  top 
of  the  tube. 

Fig.  25  represents  the  construction 
and  arrangement  of  the  chain-pump. 

644   Under  what  Circumstances  is 
the  chain-pump  generally  employed  1 

When  the  height  through  which  the  water  is  to  be 


SCIENCE   OF   COMMON,,  THINGS.    t  101 


Torricelli. 


Why  water  rises  1&  a  p'lrip* 


raised,  is  not  very  considerable,  as  in  the  case  where 
the  foundations  of  docks,  &c.,  are  to  be  drained. 

645  Who  first  ascertained  and  demonstrated  the  reason  for  the  ascent 
of  water  in  a  tube  by  suction,  and  in  the  common  pump  ? 

Torricelli,  a  pupil  of  Galileo. 

646  How  was  he  led  to  his  conclusions  ? 

He  argued,  that  whatever  be  the  cause  which  sus- 
tained a  column  of  water  in  a  common  pump,  the  mea- 
sure of  the  power  thus  manifested  must  be  the  weight 
of  the  column  of  water  ;  and  consequently,  if  another 
liquid  be  used,  heavier  or  lighter,  bulk  for  bulk,  than 
water,  then  the  same  force  must  sustain  a  lesser  or 
greater  column  of  such  liquid.  By  using  a  much 
heavier  liquid,  the 
column  sustained 
would  necessarily  be 
much  shorter,  and 
the  experiment  in 
every  way  more 
manageable. 

Torricelli  verified  his  con- 
clusions in  the  following 
manner : — He  selected  for 
his  experiment  mercury, 
the  heaviest  known  liquid. 
As  this  is  13£  times  heavier 
than  water,  bulk  for  bulk, 
it  followed  that,  if  the  force 
imputed  to  a  vacuum  could 
sustain  33  feet  of  water,  it 
would  necessarily  sustain 
13£  times  less,  or  about  30 
inches,  of  mercury.  Torri- 
celli therefore  made  the  fol- 
lowing experiment,  which 
has  since  become  memo- 
rable in  the  history  of 
science : — 

He  procured  a  glass  tube 
(Fig.  26)  more  than  30 
inches  long,  open  at  one 
end,  and  closed  at  tho 
other.  Filling  this  tube 
with  meccunr,  and  appl}'- 
ing  his  finger  to  the  open  Kg.  2«. 


102 


SCIENCE  OF   COMMON   THINGS. 


Pascal  is  experiment. 


Invention  of  the  barometer. 


end,  so  as  to  prevent  its  escape,  he  inverted  it,  plunging  the  end  into  mer- 
cury contained  in  a  vessel.  On  removing  the  linger,  he  observed  that  the 
mercury  in  the  tube  fell,  but  did  not  fall  altogether  into  the  cistern;  it 
only  subsided  until  its  surface  was  at  a  height  of  about  30  inches  above 
the  surface  of  the  mercury  in  the  cistern.  The  result  was  what  Torricelli 
expected,  and  he  soon  perceived  the  true  cause  of  the  phenomenon.  The 
weight  of  the  atmosphere  acting  upon  the  surface  of  the  mercury  in  the 
vessel,  supports  the  liquid  in  the  tube,  this  last  being  protected  from  the 
pressure  of  the  atmosphere  by  the  closed  end  of  the  tube. 

647  How  was  the  fact  that  the  column  of  mercury  was  sustained  by  the 
pressure  of  the  atmosphere  further  verified  ? 

By  an  experiment  made  by  Pascal,  in  France.  He 
argued,  that  if  the  cause  which  sustained  the  column  in 
the  tube  was  the  weight  of  the  atmosphere  acting  on 
the  external  surface  of  the  mercury  in  the  cistern,  then, 
if  the  tube  was  transported  to  the  top  of  a  high  moun- 
tain, where  a  less  quantity  of  atmosphere  was  above  it, 
the  pressure  would  be  less,  and  the  length  of  the  column 
less.  This  was  tried  and  found  to  be  the  case. 

648  How  did  these  experiments  lead  to  the  invention  of  the  barometer  f 

It  was  noticed  that  when  the  ap- 
paratus above  described  was  kept 
in  a  fixed  position,  the  height  of  the 
column  fluctuated  from  day  to  day 
within  certain  small  limits.  The 
effect  was  of  course  to  be  attributed 
to  the  variation  in  the  weight  of  the 
incumbent  atmosphere,  arising  from 
various  meteorological  causes. 

This  led  to  the  use  of  the  tube  and  cistern 
of  mercury,  arranged  in  the  manner  before 
described  (Fig.  26),  for  determining  the  changes 
in  the  atmosphere,  and  consequently  the  cha- 
racter of  the  weather. 

649  Explain  more  fully  in  what  manner 
the  barometer  can  be  used  as  a  weather-glass  ? 

When  air  is  moist,  or  filled  with 
vapor,  it  is  lighter  than  usual,  and 
the  column  of  mercury  stands  low  ; 
when  air  is  dry  and  free  from  vapor, 
it  is  heavier  than  usual,  and  the  mer- 
cury stands  high.  Thus  the  baro- 


SCIENCE   OF   COMMON   THINGS. 


103 


Wheel-barometer. 


Use  of  barometer  on  land  unreliable. 


meter  (by  showing  the  variations  in 
the  weight  of  the  air)  indicates  the 
changes  of  the  weather  also. 

650  How  is  the  common  form  of  barometer, 
called  the  wheel-barometer,  constructed  f 

The  barometer  consists  of  a  bent 
tube,  filled  with  mercury,  as  repre- 
sented in  Fig.  27,  the  column  be- 
ing sustained  by  the  pressure  of  the 
atmosphere  upon  the  surface  of  the 
mercury  in  the  shorter  arm,  the  end 
of  which  is  open.  A  small  float  of 
iron  or  glass  rests  upon  the  mercury 
in  the  shorter  arm  of  the  tube,  and 
is  suspended  by  a  slender  thread, 
which  is  passed  round  a  wheel  car- 
rying an  index.  As  the  level  of  the 
mercury  is  altered,  and  the  weight 
raised  or  lowered  in  the  tube,  the 
index  moves;  and  as  the  divisions 
on  the  circumference  of  the  circles 
within  which  it  moves  are  much 
amplified,  very  slight  changes  are 
easily  read  off. 

Fig.  27  represents  the  internal  structure  of 
the  wheel-barometer,  and  Fig.  28  its  external 
appearance,  or  casing,  with  a  thermometer 
attached.  Fjg  «;8 

651  Why  is  the  ordinary  use  of  the  barometer  on  the  land  extremely 
limited  and  uncertain? 

The  height  of  the  mercury  in  the  tube  at  any  time 
must  depend  partially  upon  the  elevation  of  the  place 
of  observation  above  the  level  of^  the  sea  ;  and  no  correct 
judgment  can  be  formed  relative  to  the  density  of  the 
atmosphere  as  affecting  the  state  of  the  weather,  with- 
out reference  to  the  situation  of  the  instrument  at  the 
time  of  making  the  observation.  Therefore,  no  atten- 
tion ought  to  be  paid  to  the  words,  "fair,  rain,  change- 
able" etc.,  frequently  engraved  on  the  plate  of  a  baro- 
meter, as  they  will  be  found  no  certain  indications  of 


104  SCIENCE   OF   COMMON   THINGS. 

Difference  between  a  thermometer  and  barometer.       Peculiarities  of  climates. 

the  correspondence  between  the  heights  marked,  and 
the  state  of  the  weather. 

653   What  is  the  difference  "between  a  thermometer  and  a  barometer? 

In  a  thermometer  the  mercury  is  sealed  up  from  the 
air ;  and  rises  or  falls  as  the  varying  temperature  of 
the  air  expands  or  contracts  it ;  but  in  a  barometer  the 
mercury  is  left  exposed  (or  open)  to  the  air  /  and  rises 
or  falls  as  the  varying  weight  ot  the  air  presses  upon 
the  open  column. 

653  Why  is  the  tube  of  a  barometer  left  open  f 

That  the  air  may  press  upon  it  freely  ;  and,  as  this 
pressure  varies,  the  mercury  rises  or  falls  in  the  tube. 

654  Why  does  the  mercury  in  the  barometer  rise  at  the  approach  of 
fair  weather  ? 

Because  the  air  is  becoming  more  dry^  and  the  drier 
the  air,  and  the  more  free  it  is  from  vapor,  the  greater 
the  pressure. 

655  Why  does  the  mercury  sink  at  the  approach  of  foul  weather  f 

Because  the  air  is  laden  with  vapor  or  disturbed  by 
wind. 

656  Why  does  vapor  in  the  air  cause  the  mercury  to  sink  f 

Because  air  containing  vapor  is  lighter  than  dry 
air  ;  and  its  pressure  on  the  mercury  is  therefore  less. 

657  Why  will  there  be  no  rain  if  the  air  be  very  dry  f 

Because  dry  air  will  absorb  moisture,  and  not  part 
with  it  in  rain. 


CIIAPTEE    YIII. 

PECULIARITIES    OF   CLIMATES. 
658    What  do  we  mean  by  the  term  climate  ? 

By  climate,  we  mean  the  condition  of  a  place  in 
relation  to  the  various  phenomena  of  the  atmosphere, 


SCIENCE   OF   COMMON   THINGS.  105 


Mean  daily  temperature.  Temperature  varies  with  the  altitude. 

as  temperature,  moisture,  etc.     Thus,  we  speak  of  a 
warm  or  cold  climate,  a  moist  or  dry  climate,  etc. 

659   What  is  meant  by  the  mean  daily  temperature  f 

The  mean  or  average  temperature  of  the  day  is 
found  by  observing  the  thermometer  at  fixed  intervals 
of  time  during  the  twenty-four  hours,  and  then  divid- 
ing the  sum  of  the  temperatures  by  the  number  of 
observations. 

6  6O  How  is  the  mean  annual  temperature  of  a  particular  point  ascer- 
tained ? 

By  taking  the  average  of  all  the  mean  daily  tempe- 
ratures throughout  the  year. 

661  How  does  temperature  vary  with  the  latitude  ? 

The  average  annual  temperature  of  the  atmosphere 
diminishes  from  the  equator  towards  either  pole. 

663  Give  examples  of  this  variation  ? 

At  the  equator,  in  Brazil,  the  average  annual  tem- 
perature is  84°  Fahrenheit's  thermometer ;  at  Calcutta, 
lat.  22°  35'  1ST.,  the  annual  temperature  is  78°  F ;  at 
Savannah,  lat.  32°  5'  N.,  the  annual  temperature  is 
65°  F. ;  at  London,  lat.  51°  31'  1ST.,  the  annual  tempe- 
rature is  50°  F. ;  at  Melville  Island,  lat,  74°  47'  1ST.,  the 
mean  annual  temperature  is  1°  below  zero. 

663  How  does  the  temperature  vary  with  the  altitude  above  the  earth's 
surface  ? 

Temperature  diminishes  with  the  altitude.  As  a 
general  rule,  a  loss  of  heat  occurs  to  the  extent  of  one 
degree  F.  for  every  343  feet  of  elevation. 

664  How  does  the  gradual  reduction  of  temperature  as  we  ascend  from 
the  surface  of  the  earth  affect  the  moisture  of  the  air  ? 

In  every  latitude  there  is  a  point  above  the  surface 
of  the  earth  where  moisture,  once  frozen,  always  re- 
mains congealed. 

665  Why  are  tlie  tops  of  very  high  mountains  always  covered  with 
snow  ? 

Because,  at  the  great  elevation  of  their  summit,  the 
temperature  of  the  atmosphere  is  so  low  that  the  con- 
gealed moisture  which  falls  upon  them  never  melts. 


106  SCIENCE  OF  COMMON   THINGS. 


What  is  a  glacier  f  Icebergs.  Line  of  perpetual  snow. 


600   What  is  a  glacier  f 

The  glacier  only  exists  upon  mountains  whose  sum- 
mits are  covered  with  perpetual  snow.  The  snow  upon 
the  higher  parts  becomes  somewhat  softened  during 
the  summer,  and  in  the  winter  is  again  hardened  nearly 
to  ice.  In  the  succeeding  summer,  the  action  of  the 
sun,  and  the  internal  heat  of  the  earth,  detach  large 
masses  loaded  with  recently  deposited  snow  into  the 
neighboring  valleys,  where,  being  accumulated,  and 
the  crevices  filled  with  snow  or  water  which  at  Jast 
hardens  to  ice,  they  form  huge  seas  of  ice,  or  a  glacier  / 
in  French,  mers-de-glace. 

667  Do  the  glaciers  continue  to  increase  year  by  year  f 

Very  many  of  them  do ;  and  in  Switzerland  many 
valleys,  once  fertile,  are  now  filled  with  glaciers.  From 
the  bottom  of  the  glacier  streams  of  water  constantly 
issue,  and  it  is  from  such  sources  that  the  rivers  Rhine 
and  Rhone  of  Europe  take  their  rise. 

668  How  are  the  gigantic  icebergs  formed  which  are  found  floating  at 
some  seasons  in  the  Atlantic  ? 

They  are  portions  of  great  glaciers  formed  in  the 
northern  regions,  which  become  detached  and  float  in 
the  sea. 

669  How  high  are  icebergs  sometimes  seen  f 

Sometimes  exceeding  300  feet  in  height. 

670  At  what  elevation  above  the  surface  of  the  earth,  at  the  equator, 
will  water  remain  frozen  ? 

At  an  elevation  of  about  15,000  jjfrf& 

671  At  what  elevation  in  the  straits  of  Magellan  will  water  remain 
frozen  f 

At  about  4000  feet. 

673   What  is  the  point  where  water  remains  frozen  called  t 

The  line  of  perpetual  snow. 

673  Why  are  not  all  places  which  lie  under  the  same  parallel  of  lati- 
tude of  the  same  temperature  ? 

Because  various  disturbing  circumstances  tend  to  vary 
the  mean  temperature. 


SCIENCE   OF   COMMON   THINGS.  107 

Effect  of  the  sea  on  the  climate.    Of  mountains  on  temperature.    Natural  soils. 

6  7*4  W  hat  disturbing  circumstances  affect  the  temperature  of  particular 
situations  f 

1.  The  elevation  and  form  of  the  land  ; 

2.  The  proximity  of  the  sea  ^ 

3.  Mountains,  swamps,  and  forests; 

4.  The  nature  of  the  soil  ;  and 

5.  The  prevalence  of  cold  or  warm  winds. 

67*5  What  effect  is  produced  on  temperature  by  the  configuration  of 
lands? 

Islands  and  peninsulas  are  warmer  than  continents  ; 
bays  and  inland  seas  also  tend  to  raise  the  mean  tem- 
perature. 

6*76   What  effect  has  the  sea  on  temperature  ? 

In  warm  climates  it  tends  to  diminish  the  heat  ;  in 
cold  climates  to  mitigate  .the  cold. 

677*   What  effect  have  mountains  on  temperature  f 

Chains  of  mountains  which  ward  off  cold  winds,  aug- 
ment the  temperature  /  but  mountains  which  ward  on 
south  and  west  winds,  lower  it. 

G7*8    What  effect  has  soil  on  temperature  ? 

A  sandy  soil,  which  is  dry,  is  warmer  than  a  marshy 
soil,  whicn  is  wet,  and  subject  to  great  evaporation. 

67*0   What  is  a  natural  soil? 

Natural  soils  are  merely  decomposed  parts  of  the  sub- 
jacent rocks,  mixed  with  the  decomposed  portion  of 
vegetable  substances  which  have  grown  or  fallen  upon 
it,  with  some  animal  substances. 

68O  What  is  the  name  given  to  the  vegetable  and  animal  products 
mixed  with  the  mineral  ingredients  of  a  soil  f 


681  What  beneficial  effect  do  loose  stones  and"  rocks  have  upon  dry 
porous  soils  ? 

They  retain  moisture  in  the  soil  by  preventing  the 
evaporation  which  would  otherwise  take  place.  In 
high  lands  they  serve  to  condense  fogs  and  low  clouds, 
and  thus  add  to  the  moisture  of  the  subjacent  soil. 

G83    What  countries  are  the  most  cloudy  f 

Those  where  the  temperature  and  winds  are  most 
variable,  as  Great  Britain. 


108  SCIENCE   OF   COMMON   THINGS. 

Where  the  most  rain  falls.  How  many  rainy  days  in  the  year. 

633  What  countries  are  the  least  cloudy  f 

Those  where  the  temperature  and  winds  are  least 
variable,  as  Egypt. 

634  Why  are  mountainous  countries  more  rainy  than  flat  ones? 

Because  the  air  (striking  against  the  sides  of  the 
mountains)  is  carried  up  the  inclined  plane,  and  brought 
in  contact  with  the  cold  air  of  the  higher  regions ;  in 
consequence  of  which  its  vapor  is  condensed  and  depo- 
sited in  rain. 

635  When  is  the  quantity  of  moisture  in  the  air  greatest,  and  when 
least? 

It  is  greatest  in  the  summer  months,  and  least  in  the 
winter. 

686  In  what  part  of  the  world  does  rainfall  most  abundantly  f 

Near  the  equator  /  and  the  quantity  of  rain  decreases 
as  we  approach  the  poles. 

637*  How  many  inches  of  rain  faU  yearly  at  tlie  city  of  Vera  Cruz, 
Mexico  ? 

About  two  hundred  and  seventy-eight  inches. 

633  How  great  a  depth  of  rain,  measured  in  inches,  falls  yearly  in 
London f 

•About  twenty-Jive  inches 

689  How  do  you  account  for  the  great  amount  of  rain  falling  at  Vera 
Cruz  f 

Vera  Cruz,  situated  within  the  tropics,  is  backed  by 
lofty  mountains,  whose  summits  are  covered  with  per- 
petual snow  j  against  these  the  hot,  humid  air  from 
the  sea  is  driven  by  the  trade-winds,  condensed,  and  its 
excess  of  moisture  is  precipitated  as  rain. 

690  In  what  latitudes  do  the  greatest  number  of  rainy  days  occur  f 

There  are  more  rainy  days  in  the  temperate  zones 
than  in  the  tropics,  although  the  yearly  quantity  of 
rain  falling  in  the  latter  districts  is  much  greater  than 
in  the  former. 

691  About  how  many  rainy  days  are  there  in  a  year  in  the  northern 
parts  of  the  United  States  ? 

About  one  hundred  and  thirty-four ;  in  the  South- 
ern States  the  number  is  somewhat  less,  being  about 
one  hundred  and  three. 


SCIENCE   OF   COMMON   THINGS.  109 

Ilain-gauge.  "Wet  and  dry  seasons  of  the  tropics. 

693  Why  does  it  rain  more-  frequently  in  the  temperate  zones  than  in 
the  tropics  f 

Because  the  temperate  zone  is  a  region  of  variable 
winds,  and  the  temperature  of  the  atmosphere  changes 
often  ;  while  in  the  tropics  the  wind  changes  but  rarely, 
and  the  temperature  is  very  constant  throughout  a  great 
part  of  the  year. 

693  How  is  the  amount  of  rain  measured  f 

By  means  of  a  rain-gauge. 

694:  How  is  this  constructed  ? 

The  best  form  consists  of  a  cylindrical  metal  vessel 
furnished  with  a  float ;  the  rain  falling  into  the  vessel 
raises  the  float,  the  stem  of  which  is  so  graduated  that 
the  increase  in  depth  can  be  very  accurately  measured. 

695  Why  does  it  rain  more  upon  the  sea-coast  than  in  the  interior  of 
a  country  ? 

Because  the  air  adjacent  to  the  ocean  contains  more 
moisture  than  the  air  inland. 

696  What  is  the  average  yearly  fall  of  rain  in  the  tropics  and  tempe- 
rate zones  ? 

The  average  yearly  fall  of  rain  in  the  tropics  is  nine- 
ty-five inches  ;  in  the  temperate  zone  only  thirty-five. 

The  greatest  rain-fall,  however,  is  precipitated  in  the  shortest  time. 
Ninety -five  inches  fall  in  eighty  days  on  the  equator,  while  'at  St.  Peters- 
burg the  yearly  rain-fall  is  but  seventeen  inches,  spread  over  one  hundred 
and  sixty-nine  days.  Again,  a  tropical  wet  day  is  not  continuously  wet. 
The  morning  is  clear ;  clouds  form  about  ten  o'clock  ;  the  rain  begins  at 
twelve,  and  pours  till  about  half-past  four;  by  sunset  the  clouds  are 
gone,  and  the  nights  are  invariably  fine. 

697*  In  the  tropics,  how  are  the  seasons  divided? 

Into  the  wet  or  rainy,  and  the  dry  season. 

698  Are  there  some  countries  entirely  destitute  of  rain  ? 

In  some  parts  of  Egypt  it  never  rains ;  in  Peru  it 
rains  once,  perhaps,  in  a  man's  lifetime. 

Upon  the  table-land  of  Mexico,  in  parts  of.  Guatemala  and  California, 
for  the  same  reason,  rain  is  very  rare.  But  the  grandest  rainless  districts 
are  those  occupied  by  the  great  desert  of  Africa,  extending  eastward 
over  portions  of  Arabia  and  Persia  to  a  desert  province  of  the  Belooches — 
districts. farther  continued  in  the  heart  of  Asia  over  the  great  desert  of 
Gobi,  the  table-land  of  Thibet,  and  part  of  Mongolia.  In  all  these  are 
five  or  six  millions  of  square  miles  of  land  that  never  taste  a  shower. 


110  SCIENCE  OF  COMMON  THINGS. 

Countries  destitute  of  rain.        Aunual  amount  of  rain.        Annual  eva'poration. 
6Q9    Why  are  these  countries  destitute  of  rain  ? 

The  cause  of  this  scarcity  is  to  be  sought  for  in  the 
peculiar  conformation  of  the  country. 

In  Peni,  parallel  to  the  coast,  and  at  a  short  distance  from  the  sea,  is 
the  lofty  range  of  the  Andes,  the  peaks  of  which  are  covered  with  per- 
petual snow  and  ice.  The  prevailing  wind  is  an  east  wind,  sweeping 
from  the  Atlantic  to  the  Pacific  across  the  continent  of  South  America. 
As  it  approaches  the  west  coast,  it  encounters  this  range  of  mountains, 
and  becomes  so  cooled  by  them  that  it  is  forced  to  precipitate  its  moist- 
ure and  passes  on  to  the  coast  almost  devoid  of  moisture.  In  Egypt  and 
other  desert  countries,  the  dry  sandy  plains  heat  the  atmosphere  to  such 
an  extent  that  it  absorbs  moisture,  and  precipitates  none. 

7OO  Are  there  some  districts  in  which  it  may  be  said  to  always  rain  ? 

In  some  portions  of  Guiana  it  rains  for  'a  great  por- 
tion of  the  year.  The  fierce  heat  of  the  tropical  sun 
fills  the  atmosphere  with  vapor,  which  returns  to  the 
earth  again  in  constant  showers,  as  the  cool  winds  of  the 
ocean  flow  in  from  the  higher  latitudes. 

7*O1  How  great  a  quantity  of  water  is  supposed  to  be  annually  precipi- 
tated as  rainf 

The  amount  is  calculated  to  exceed  seven  hundred 
and  sixty  millions  of  tons 

7*OJ3   Was  this  whole,  amount  raised  by  evaporation  into  the  atmosphere  f 

Certainly ;  the  daily  amount  of  water  raised  by 
evaporation  from  the  sea  alone  amounts  to  no  less  than 
one  hundred  and  sixty-four  cubic  miles,  or  about  sixty 
thousand  cubic  miles  annually. 

7*O3  What  is  the  daily  amount  of  evaporation  from  the  sea  between  the 
Cape  of  Good  Hope  and  Calcutta  f 

During  the  months  of  October  and  November,  it  is 
known  to  average  three  quarters  of  an  inch  daily  from 
the  wrhole  surface. 

7*04  Is  the  climate  of  New  England  and  the  Northern  United  States 
drier  than  that  of  England  and  Central  Europe  ? 

It  is  /  and  this  fact  exercises  an  important  influence 
upon  many  professions  and  callings,  tainters  find  that 
their  work  dries  quicker  in  New  England  than  in  Cen- 
tral Europe.  Cabinet-makers  here  are  obliged  to  use 
thicker  glue,  and  watchmakers  animal  instead  of  vege- 
table oil. 


SCIENCE   OF   COMMON   THINGS.  Ill 


Hail-storms,  where  most  frequent.  The  moon  and  the  weather. 


7*O5  Why  will  not  pianofortes  made  in  England  or  Germany  answer 
for  use  in  New  England  ? 

Because  the  difference  in  the  climate  of  these  respec- 
tive countries  is  so  great,  as  respects  moisture,  that 
the  foreign  instruments  shrink,  and  quickly  become 
damaged. 

7O  6  In  what  climates  do  hail-storms  most  frequently  occur  f 

In  temperate  climates  most  frequently,  and  rarely 
within  the  tropics. 

707  In  what  localities  in  the  temperate  zones  do  hail-storms  occur  most 
frequently  1 

In  the  vicinity  of  high  mountains,  whose  peaks  are 
always  covered  with  ice  and  snow.  The  south  of  France, 
which  lies  between  the  Alps  and  Pyrenees,  is  annually 
ravaged  by  hail  ;  and  the  damage  which  it  causes 
yearly  to  vineyards  and  standing  crops,  is  estimated  at 
upwards  of  nine  millions  of  dollars. 


Do  the  general  meteorological  changes  which  take  place  almost 
daily,  and  which  are  designated  as  weather  changes,  occur  in  accordance 
with  certain  fixed  laws  f 

There  is  no  reason  to  doubt  that  every  change  in  the 
weather  is  in  strict  accordance  with  some  certain  phy- 
sical agencies,  which  are  fixed  and  certain  in  their 
operations. 

7*09  Why  can  we  not,  then,  with  certainty  determine  and  foretell  the 
character  of  the  weather  for  any  particular  time  ? 

Because  the  laws  which  govern  meteorological 
changes  are  as  yet  imperfectly  understood. 

7*1O  Is  there  any  reason  for  supposing  that  the  moon  has  any  influence 
upon  the  weather  f 

An  examination  of  meteorological  records,  kept  in 
different  countries  through  many  years,  proves  conclu- 
sively that  the  popular  notions  concerning  the  influence 
of  the  lunar  phases  on  the  weather  have  no  foundation 
in  any  well  established  theory,  and  no  correspondence 
with  observed  facts. 

7*11  Do  meteorological  records  afford  any  support  to  the  belief  in  tha 
occurrence  of  rain  at  particular  phases  of  the  moon  ? 

There  is  some  reason  for  supposing  that  rain  falls 


112  SCIENCE    OF   COMMON   THINGS. 


Effect  of  moonlight  on  animals  and  vegetables.  Equinoctial  storm. 

more  frequently  about  four  days  before  full  moon,  and 
less  frequently  about  four  or  five  days  before  new 
moon,  than  at  other  parts  of  the  month ;  but  this  can- 
not be  considered  as  an  established  fact :  in  other 
respects  the  changes  of  the  moon  cannot  be  shown  to 
have  influenced  in  any  way  the  production  of  rain. 

713  Does  the  bright  moonlight  in  any  ivay  hasten  the  putrefaction  of 
animal  or  vegetable  substances  ? 

It  is  generally  supposed  to  do  so ;  but  the  fact  is, 
that-  on  bright,  clear  nights,  when  the  moon  shines 
brilliantly,  dew  is  more  freely  deposited  on  these  sub- 
stances than  'at  other  times,  and  in  this  way  putrefac- 
tion may  be  accelerated.  With  this  the  moon  has  no 
connexion. 

713  Is  there  any  foundation  for  the  belief  that  the  appearance  of  the 
aurora  borealis  is  followed  by  a  change  in  tlie  weather? 

Meteorological  registers  conclusively  showT  that  there 
is  no  such  connexion,  and  that  the  appearance  of  the 
aurora  is  as  often  followed  by  fair  weather  as  by  foul. 

714  Is  there  any  truth  in  the  traditional  notion  that  a  long  and  violent 
storm  usually  accompanies  the  period  of  the  equinoxes  ? 

The  examination  of  weather-records  for  sixty-four 
years  shows  that  no  particular  day  can  be  pointed  out 
in  the  month  of  September,  (when  the  "  equinoctial 
storm  "  is  said  to  occur)  upon  which  there  ever  was,  or 
ever  will  be,  a  so-called  equinoctial  storm.  The  fact, 
however,  should  not  be  concealed,  that  taking  the  ave- 
rage of  the  five  days  embracing  the  equinox  for  the 
period  above  stated,  the  amount  of  rain  is  greater  than 
for  any  other  five  days,  by  three  per  cent.,  throughout 
the  month. 

715  Is  there  any  reason  for  believing  that  cold  and  warm  seasons  alter- 
nate? 

Meteorological  records,  kept  for  eighty  years  at  the 
observatory  of  Greenwich,  England,  seem  to  show  that 
groups  of  warm  years  alternate  with  cold  ones  in  such 
a  way  as  to  render  it  most  probable  that  the  mean  an- 
nual temperatures  rise  and  fall  in  a  series  of  curves, 
corresponding  to  periods  of  about  fourteen  years. 


SCIENCE  OF   COMMON  THINGS.  113 

Can  animals  foretell  changes  in  the  weather  ? 


7*1(3  Is  it  probable  that  some  animals  and  insects  are  able  to  foretell 
changes  in  the  weather  before  man  can  perceive  any  indications  of  the  same  ? 

Of  this  fact  there  appears  to  be  no  doubt.  Some 
varieties  of  the  land-snail  only  make  their  appearance 
'before  a  rain.  Some  other  varieties  of  land  crustaceous 
animals  change  their  color  and  appearance  twenty-four 
hours  before  a  rain. 

7*17*  What  curious  fact  has  been  noticed  in  respect  to  the  leaves  of.  trt™ 
indicating  changes  in  the  iveather  ? 

For  a  light,  short  rain,  some' trees  have  been  observed 
to  incline  their  leaves,  so  as  to  retain  water  /  but  for  a 
long  rain,  they  are  so  doubled  as  to  conduct  the  water 
away. 

7*18  What  fact  has  also  been  noticed  respecting  the  changes  in  springs 
previous  to  a  rain  ? 

The  water  of  springs  has  been  observed  to  rise  and 
flow  out  in  greater  volume  previous  to  a  rain. 

Most,  if  not  all,  of  the  popular  proverbs  respecting  changes  in  the  wea- 
ther, the  influence  of  the  moon,  of  frosts,  auroras,  and  the  like,  when 
tested  by  observation,  will  be  found  to  be  unsupported  by  facts,  and 
unworthy  of  the  slightest  credence. 

7*19    Why  will  there  be  no  rain  if  the  air  be  very  cold  f 

Because  it  is  so  muck  condensed  that  it  has  already 
parted  with  as  much  moisture  as  it  can  spare. 

7*2O  Have  heat  and  cold  any  effect  on  the  barometer  f 

No,  not  of  themselves  ;  but  as  cold  weather  is  gene- 
rally either  dry  or  rough,  with  northerly  winds,  the 
mercury  generally  rises  in  cold  weather ;  and  as  warm 
weather  is  often  moist,  or  accompanied  by  southerly 
winds,  which  bring  vapor  with  them,  therefore  the  mer- 
cury often  sinks  in  warm  weather. 


114:  SCIENCE    OF   COMMON   THINGS. 


Production  of  sound.  Drum  of  the  ear. 


PART  IV. 

SOUND. 

CHAPTEK   I. 

ORIGIN   AND   TRANSMISSION   OF   SOUND. 


How  is  sound  produced  f 

Sound  is  heard  when  any  sudden  shock  or  impulse, 
causing  vibrations,  is  given  to  the  air,  or  any  other 
body,  which  is  in  contact  directly  or  indirectly  with  the 
drum  of  the  ear. 

T22    What  is  the  drum  or  tympanum  of  the  ear  ? 

A  thin  membrane  which  closes  the  aperture  of  the 
ear. 

7*23  How  do  the  vibrations  of  the  air,  striking  upon  the  drum  of  the  ear, 
give  us  the  sensation  of  sound  ? 

Behind  the  drum  of  the  ear  are  various  cavities  and 
tubes  in  the  bone  which  form  the  side  of  the  head,  in 
which  the  minute  fibres  of  the  auditory  nerve  are  dis- 
tributed. When  the  drum  of  the  ear  is  made  to  vibrate 
freely  .by  the  action  of  the  sonorous  undulations  of  the 
external  air,  the  vibrations  are  communicated  by  the 
action  of  minute  bones,  nmscles,  and  fluids  contained  in 
the  cavities  of  the  ear,  to  the  nerve,  and  from  thence  the 
impressions  are  conveyed  to  the  brain. 

Fig.  29  is  a  perspective  magnified  view  of  the  interior  of  the  ear.  The 
several  parts  of  the  ear,  and  the  progress  of  sound  towards  the  nerve 
which  communicates  the  sensation  to  the  brain,  may,  however,  be  best 
illustrated  by  reference  to  Fig.  30  :  — 

1.  There  is  external  to  the  head  a  wide-mouthed  tube,  or  ear-trumpet, 
<$,  for  catching  and  concentrating  the  waves  of  sound.  It  is  movable  in 


SCIENCE    OF   COMMON   THINGS. 


115 


Construction  of  the  ear. 


Air  not  necessary  to  sound. 


fig.  29. 


Fig.  30. 


many  animals,  so  that  they  can  direct  it  to  the  place  from  which  the 
sound  comes. 

2.  The  sound  concentrated  at  the  bottom  of  the  ear-tube  falls  upon  a 
membrane  stretched  across  the  channel,  like  the  parchment  of  an  ordi- 
nary drum,  over  the  space  called  the  tympanum,  or  drum  of  the  ear,  b, 
and  causes  the  membrane  to  vibrate.      That  its  motion  may  be  free, 
the  air  contained  within  the  drum  has  free  communication  with  the 
external  air  by  the  open  passage,  /,  called  the  eustachian  tube,  leading  to 
the  back  of  the  mouth.     A  degree  of  deafness  ensues  when  this  tube  is 
obstructed,  as  in  a  cold ;  and  a  crack,  or  sudden  noise,  with  immediate 
return  of  natural  hearing,  is  generally  experienced  when,  in  the  effort  of 
sneezing  or  otherwise,  the  obstruction  is  removed. 

3.  The  vibrations  of  the  membrane  of  the  drum  are  conveyed  further 
inwards,  through  the  cavity  of  the  drum,  by  a  chain  of  four  bones  (not 
here   represented   on   account  of  their  minuteness),  reaching  from  the 
centre  of  the  membrane  to  the  oval  door  or  window,  leading  into  the 
labyrinth  e. 

4.  The  labyrinth,  or  complex  inner  compartment  of  the  ear,  over  which 
the  nerve  of  hearing  is  spread  as  a  lining,  is  full  of  watery  fluid ;  and, 
therefore,  by  the  law  of  fluid  pressure,  when  the  force  of  the  moving 
membrane  of  the  drum,  acting  through  the  chain  of  bones,  is  made  to 
compress  the  water,  the  pressure  is  felt  instantly  over  the  whole  cavity. 
The  labyrinth  consists  of  the  vestibuk,  e,  the  three  semicircular  canals,  c, 
imbedded  in  the  hard  bone,  and  a  winding  cavity,  called  the  cochlea,  d, 
like  that  of  a  snail-shell,  in  which  fibres,  stretched  across  like  harp-strings, 
constitute  the  lyra.     The  separate  uses  of  these  various  parts  are. not  yet 
fully  known.     The  membrane  of  the  tympanum  may  be  pierced,  and  the 
chain  of  bones  may  be  broken,  without  entire  loss  of  hearing. — ARNOTT. 

*7S4:  Is  air  necessary  to  the  production  of  sound  ? 

'  No  ;  but  most  sounds  owe  their  origin  to  the  vibra- 
tions of  the  air.  Sound  can  be  produced  under  water, 
and  all  bodies  are,  in  fact,  more  or  less  fitted  to  produce 
the  sound  vibrations  ;  in  many  cases  air  is  neither  the 
quickest  nor  the  best  conductor  of  sound. 

735  Upon  what  does  the  loudness  of  sound  conveyed  by  air  depend  f 

Upon  the  density  of  the  air  ? 


SCIENCE   OF   COMMON   THINGS. 


What  is  a  sonorous  body  ?  Sonorous  vibrations.  Bell  metal. 


Why  does  a  bell  rung  in  a  receiver  exhausted  of  air  fail  to  produce 
sound  ? 

Because  no  air  is  present  to  receive  and  transmit  the 
vibrations. 

7*37*   What  is  a  sounding  or  sonorous  body  f 

A  body  possessing  both  hardness  and  elasticity, 
which,  when  struck,  vibrates,  and  imparts  to  the  air  in 
contact  with  it  undulations  corresponding  to  its  vibra- 

tions. 

7*38  Why  has  the  peculiar  kind  of  motion  in  bodies  which  gives  rise  to 
the  sensation  of  sound,  been  termed  vibration  ? 

Because  a  striking  analogy  may  be  traced  between 
the  tremulous  agitation  which  takes  place  among  the 
particles  of  a  sounding  body  and  the  oscillations  of  a 
pendulum. 

7*30  How  'may  the  nature  of  sonorous 
vibrations  be  illustrated  f 

By  noticing  the  visible  mo- 
tions which  occur  on  striking 
or  twitching  a  tightly  extender 
cord  or  wire.     Suppose  such  a 
cord,  represented  by  the  cen-  Flg  31 

tral   line   in   Fig.    31,    to   be 

forcibly  drawn  out  to  A,  and  let  go  ;  it  would  immedi- 
ately recover  its  original  position  by  virtue  of  its  elas- 
ticity ;  but  when  it  reached  the  central  point,  it  would 
have  acquired  so  much  momentum  as  would  cause  it  to 
pass  onward  to  a  ;  thence  it  would  vibrate  back  in  the 
same  manner  to  B,  and  back  again  to  5,  the  extent  of 
its  vibration  being  gradually  diminished  by  the  resist- 
ance of  the  air,  so  that  it  would  at  length  return  to  a 
state  of  rest. 

7*30   Why  are  copper  and  iron  sonorous,  and  not  lead  ? 

Copper  and  iron  are  hard  and  elastic  /  but  as  lead 
is  neither  hard  nor  elastic,  it  is  not  sonorous. 

731   Of  what  is  bell-metal  made  f 

Of  copper  and  tin  in  the  following  proportions  :  —  In 
every  five  pounds  of  bell-metal  there  should  be  one 
pound  of  tin  and  four  pounds  of  copper. 


SCIENCE   OF  COMMON   THINGS.  117 

Solids  transmit  sound.         The  earth  conducts  sound.         Sound  vibrations. 


73S   Why  is  this  mixture  of  tin  and  copper  used  for  bell-metal  ? 

Because  it  is  much  harder  and  more  elastic  than  any 
of  the  pure  metals. 

733  Are.  solids  capable  of  transmitting  sounds  f 

All  solid  bodies  which  possess  elasticity  have  the 
power  of  propagating  or  transmitting  sounds. 

734  What  easy  experiment  illustrates  the  transmission  of  sound  by 
solids  f 

When  a  stick  is  held  between  the  teeth  at  one  ex- 
tremity, and  the  other  is  placed  in  contact  with  a  table, 
the  scratch  of  a  pin  on  the  table  may  be  heard  with 
great  distinctness,  though  both  ears  be  stopped. 

735  Does  tfie  earth  conduct  sound  f 

The  earth  often  conducts  sound,  so  as  to  render  it 
sensible  to  the  ear,  when  the  air  fails  to  do  so.  It  is 
well  known  that  the  approach  of  a  troop  of  horse  can 
be  heard  at  a  distance  by  putting  the  ear  to  the  ground, 
and  savages  practise  this  method  of  ascertaining  the 
approach  of  persons  from  a  great  distance. 

73Q    What  purpose  is  subserved  by  tJie  body  of  a  stringed  instrument  t 

The  string  of  an  instrument,  when  caused  to  vibrate, 
communicates  the  vibrations  to  the  matter  composing 
the  body  of  the  instrument  and  the  surrounding  air, 
and  thus  a  tone  or  musical  note  is  produced  and  ren- 
dered audible  to  the  ear. 

737  How  are  aerial  vibrations  or  pulses  communicated? 

The  air,  encompassing  sounding  bodies  on  every  side, 
conveys  the  sensation  of  sound  in  all  directions  ;  there- 
fore the  aerial  vibrations,  or,  as  they  have  been  termed, 
"pulses"  must  be  communicated  successively  and  ge- 
nerally throughout  the  whole  space  within  the  limits 
of  which  they  are  capable  of  affecting  the  ear. 

738  To  what  have  the  sound  vibrations  or  pulsations  been  compared? 

To  the  waves  spreading  in  concentric  circles  over 
the  smooth  surface  of  water. 

"When  a  stone  is  thrown  into  water,  the  liquid  waves  are  propagated 
not  only  directly  forward  from  the  centre,  but  if  they  encounter  any  obr 
struction,  as  from  a  floating  body,  they  will  bend  their  course  round  the 
sides  of  the  obstacle,  and  spread  out  obliquely  beycm4  it.  So  th,e  undu. 

6 


118  SCIENCE   OF  COMMON   THINGS. 


Sound  vibrations  may  be  rendered  visible.  Telocity  of  sound. 


lations  of  air,  if  interrupted  in  their  progress  by  a  high  wall  or  other  simi- 
lar impediment,  will  be  continued  over  its  summit  and  propagated  on  the 
opposite  side  of  it. 

739  When  a  sonorous  body  is  struck,  do  all  the  particles  of  which  it  it 
composed  really  move  or  vibrate  ? 

They  do  ;  and  the  body  itself,  no  matter  how  com- 
pact and  solid  it  may  be,  really  changes  its  form  with 
each  vibration. 

740  How  may  the  sound  vibrations  in  a  solid  body  be  rendered  visible  f 

By  many  simple  contrivances  —  as  by  a  ball  hung  by 
a  string  to  a  bell,  by  pieces  of  paper  placed  on  the 
strings  of  a  violin,  or  by  sand  placed  upon  the  sound- 
ing-board of  a  piano  or  any  other  stringed  instrument. 

741  How  fast  does  sound  travel  f 

About  13  miles  in  a  minute,  or  1142  feet  in  a  second 
of  time. 


Why  is  the  flash  of  a  gun  fired  at  a  distance  seen  long  before  th« 
report  is  heard  ? 

Because  light  travels  much  faster  than  sound. 

Light  would  go  480  times  round  the  whole  earth  while  sound  is  going 
its  13  miles. 

743  How  is  a  knowledge  of  the  velocity  of  sound  made  applicable  to  the 
measurement  of  distances  f 

Suppose  a  flash  of  lightning  to  be  perceived,  and  on 
counting  the  seconds  that  elapse  before  the  thunder  is 
heard,  we  find  them  to  amount  to  3£  ;  then  as  sound 
moves  1142  feet  in  a  second,  it  will  follow  that  the 
thunder-cloud  must  be  distant  1142  x  3£  =  3997  feet. 

744  Why  do  windows  rattle  when  carts  pass  by  a  house  ? 

1.  Because  glass  is  sonorous  •  and  the  air  communi- 
cates its  vibrations  to  the  glass,  which  echoes  the  same 
sound  ;  and 

2.  The  window-frame  being  shaken,  contributes  to 
the  noise. 

"Window-frames  are  shaken,  1.  By  sound-waves  striking  against  them. 
2.  By  a  vibratory  motion  communicated  to  them  by  the  walls  of  the 
house. 

745  Why.  is  the  sound  of  a  bell  stopped  by  touching  the  bell  with  our 
finger  f 

Because  the  weight  of  our  finger  stops  the  vibratiima 


SCIENCE   OF   COMMON   THINGS.  119 


How  sound  is  obstructed.  Sounds  more  distinct  by  night  than  by  day. 


of  the  bell ;  and  as  soon  as  the  bell  ceases  to  vibrate,  it 
ceases  to  make  sound-waves  in  the  air. 

7*46    Why  does  a  split  bell  make  a  hoarse,  disagreeable  sound  f 

Because  the  split  of  the  bell  causes  a  double  vibration  / 
and  as  the  sound-waves  clash  and  jar,  they  impede 
each  other's  motion,  and  produce  discordant  sounds. 

7*47'  Why  can  persons,  living  a  mile  or  two  from  town,  hear  the  bells 
of  the  town  churches  sometimes  and  not  at  others  f 

Because  fogs,  rain,  and  snow  obstruct  the  passage  of 
sound ;  but  when  the  air  is  cold  and  clear,  sound  is 
propagated  more  easily. 

7*48  Why  can  we  not  hear  sounds  (as  those  of  distant  church  bells')  in 
rainy  weather  so  well  as  in  fine  weather  ? 

Because  the  falling  rain  interferes  with  the  undula- 
tions of  the  sound-waves,  and  breaks  them  up. 

7*49  Why  can  we  not  hear  sounds  (as  those  of  distant  church  bells)  in 
snowy  weather  so  well  as  in  fine  ivealher? 

Because  the  falling  snow  interferes  with  the  undula- 
tions of  the  sound-waves,  and  stops  their  progress. 

7*5O  Why  can  we  not  hear  sounds  (such  as  those  of  distant  clocks)  so 
distinctly  in  a  thick  mist  or  haze  as  in  a  clear  night  ? 

Because  the  air  is  not  of  uniform  density  when  it  is 
laden  with  mist;  in  consequence  of  which  the  sound 
waves  are  obstructed  in  their  progress. 

7*51    Why  do  we  hear  sounds  better  by  night  than  by  day? 

1.  Because  night  air  is  of  more  uniform  density,  and 
less  liable  to  accidental  currents ;  and. 

2.  Night  is  more  still,  from  the  suspension  of  business 
and  hum  of  men.     Many  sounds  become  perceptible 
during  the  night,  which  during  the  day  are  completely 
stifled,  before  they  reach  the  ear,  by  the  din  and  dis^ 
cordant  noises  of  labor,  business,  and  "pleasure. 

7*53  Why  is  tlie  air  of  more  uniform  density  by  night  than  it  is  by 
dayf 

Because  it  is  less  liable  to  accidental  currents  ;  inas  • 
much  as  the  breezes  (created  by  the  action  of  the  sun's 
rays)  generally  cease  during  the  night. 

753  How  should  partition  walls  be  made,  to  prevent  the  voices  in  adjoin' 
ing  rooms  from  being  heard  ? 


120  SCIENCE   OF   COMMON   THINGS. 

Best  conductors  of  sound.  Musical  sounds.  "What  is  a  noise  ? 

The  space  between  the  laths  should  be  filled  with 
shavings  or  sawdust ;  and  then  no  sound  would  ever 
pass  from  one  room  to  another. 

7*54  Why  should  shavings  or  sawdust  .prevent  the.  transmission  of  sound 
from  room  to  room  ? 

Because  there  would  be  several  different  media  for 
the  sound  to  pass  through  ;  and  every  change  of  medium 
diminishes  the  strength  of  the  sound- waves. 

7*55   What  solids  are  among  the  best  conductors  of  sound  f 

Iron  and  glass  ;  sound  is  transmitted  by  them  at  the 
rate  of  17,500  feet,  or  more  than  3  miles  in  a  second ; 
after  these  rank  copper,  several  different  kinds  of  wood, 
silver,  tin,  &c. 


CIIAPTEK    II. 

VOCAL   AND   MUSICAL    SOUNDS. 
7*50    What  is  a  musical  sound? 

A  musical  sound  is  produced  by  regular  undulations 
or  vibrations — a  succession  of  sounds  following  each 
other  with  perfect  uniformity. 

7*57*  How  does  a  noise  differ  from  a  musical  sound  f 

A  noise  is  the  result  of  very  irregular  or  disturbed 
undulations  or  vibrations. 

7*58  Do  all  persons  hear  sounds  alike  f 

The  faculty  of  hearing  depends  upon  the  construc- 
tion and  sensibility  of  the  ear,  and  as  this  differs  in  dif- 
ferent individuals,  it  is  certain  that  all  persons  will  not 
hear  sounds  alike. 

7*59    What  is  meant  by  the  terms  concord  and  discord  f 

When  two  tones  or  notes  sounded  together  produce 
an  agreeable  effect  on  the  ear,  their  combination  is 


SCIENCE   OF   COMMON   THINGS.  121 

Scale  of  music.  Sounds  of  Instruments.  How  birds  sing. 

called  a  musical  concord ;  when  the  effect  is  disagree- 
able, it  is  called  a  discord. 

7*  GO   What  is  the  gamut  or  diatonic  scale  of  music  ? 

It  consists  of  seven  notes,  which  are  distinguished  by 
the  seven  first  letters  of  the  alphabet,  or  by  the  seven 
syllables,  do,  re,  mi,  fa,  sol,  la,  si. 

7*61   Why  do  flutes,  etc.,  produce  musical  sounds  1 

Because  the  breath  of  the  performer  causes  the  air 
in  the  flute  to  vibrate  /  and  this  vibration  sets  in  mo- 
tion the  sound-waves  of  the  air. 

7*03   Why  does  a,  fiddle-string  give  a  musical  sound  f 

Because  the  bow  drawn  across  the  string  causes  it  to 
vibrate  ;  and  this  vibration  of  the  string  sets  in  motion 
the  sound-waves  of  the  air,  and  produces  musical  notes. 

7*63   Why  does  a  drum  sound  t 

Because  the  parchment  head  of  the  drum  vibrates 
from  the  blow  of  the  drum-stick,  and  sets  in  motion  the 
sound-waves  of  the  air. 

7*64   Why  do  pianofortes  produce  musical  sounds  ? 

Because  each  key  of  the  piano  (being  struck  with  the 
finger)  lifts  up  a  little  hammer  which  knocks  against  a 
string  /  and  the  vibration  thus  produced  sets  in  motion 
the  sound-waves  of  the  air. 

7*35    Why  is  an  instrument  flat  when  the  strings  are  unstrung? 

Because  the  vibrations  are  too  slow  /  in  consequence 
of  which  the  sounds  produced  are  not  shrill  or  sharp 
enough. 

7*©S   Why  do  birds  alone,  of  animals,  produce  musical  notes  f 

Because  they  alone  are  gifted  with  a  vocal  organiza- 
tion, which  enables  them  to  produce  musical  notes.  In 
other  animals,  the  larynx  is  placed  wholly  at  the 
upper  end  of  the  windpipe  ;  but  in  birds  it  is  sepa- 
rated, as  it  were,  into  two  parts,  one  placed  at  each 
extremity. 

7*67*   Why  cannot  birds  be  so  correctly  said  to  sing  as  to  whistle  f 

Because  natural  singing  is  an  exclusive  privilege  of 
man. 


122  SCIENCE   OP   COMMON   THINGS. 

The  windpipe.  Larynx.  What  is  coughing  ? 

768/71  the  human  system,  what  are  the  parts  concerned  in  the  produc- 
tion of  speech  and  music  ? 

They  are  the  windpipe,  the  larynx,  and  the  glottis. 

769  What  is  the  windpipe  f 

The  windpipe  is  merely  a  cartilaginous  canal  through 
which  the  air  issues  from  the  lungs. 

770  What  is  the  larynx  f 

The  larynx  is  an  enlarged  continuation  of  the  wind- 
pipe, formed,  like  it,  of  cartilage  or  gristle,  membrane, 
and  muscle  y  it  is,  however,  more  complicated,  ter- 
minating above  in  two  lateral  membranes  which 
approach  near  together,  leaving  an  oblong,  narrow 
opening,  called  the  glottis. 

771  How  is  sound  produced  by  the  organs  of  voice  ? 

The  air  expired  from  the  lungs,  passes  through  tLe 
windpipe  and  out  at  the  larynx,  through  the  opening- 
of  the  membrane  called  the  glottis.  The  vibration  of 
these  membranes,  caused  by  the  passage  of  air,  causes 
sound. 

77S  How  can  the  tones  of  the  voice  be  made  grave  or  acute  f 

By  varying  the  tension  of  these  membranes  and  the 
size  of  the  opening. 

773  What  is  the  force  exerted  by  the  healthy  chest  in  blowing  f 

About  one  pound  on  the  inch  of  its  surface  ;  that 
is  to  say,  the  chest  can  condense  its  contained  air  with 
that  force,  and  can  therefore  blow  through  a  tube  the 
mouth  of  which  is  ten  feet  under  the  surface  of  water. 

774  What  is  the  vocal  action  of  coughing  ? 

In  coughing  the  top  of  the  windpipe  or  the  glottis  is 
closed  for  an  instant,  during  which  the  chest  is  com- 
pressing and  condensing  its  contained  air ;  and  on  the 
glottis  being  opened,  a  slight  explosion,  as  it  were,  of 
the  compressed  air  takes  place,  and  blows  out  any  irri- 
tating matter  that  may  be  in  the  air-passages. 

775  Why  does  a  popgun  make  a  loud  report  when  the  paper  bullet  is 
discharged  from  it? 

Because  the  air  confined  between  the  paper  bullet 
and  the  discharging  rod  is  suddenly  liberated,  and 


SCIENCE   OF   COMMON  THINGS  123 

"  What  is  sneezing?  Laughing.  Crying.  Suffocation. 

strikes  against  the  surrounding  air  ;  this  makes  a  report 
in  the  same  way  as  when  any  two  solids  (such  as  your 
hand  and  the  table)  come  into  collision. 

77©   What  is  sneezing  f 

Sneezing  is  a  phenomenon  resembling  cough ;  only 
the  chest  empties  itself  at  one  effort,  and  chiefly 
through  the  nose,  instead  of  through  the  mouth,  as  in 
coughing. 

777   What  is  laughing! 

Laughing  consists  of  quickly  repeated  expulsions  of 
air  from  the  chest,  the  glottis  being  at  the  time  in  a 
condition  to  produce  voice ;  but  there  is  not  between 
the  expirations,  as  in  coughing,  a  complete  closure  of 
the  glottis. 

773   What  is  hiccough  f 

Hiccough  is  the  stopping  of  the  commencement  of  a 
strong  inspiration,  by  a  sudden  closing  of  the  glottis. 

779  What  is  crying  ? 

Crying  differs  from  laughing  almost  solely  in  the 
circumstance  of  the  intervals  between  the  gusts  or  expi- 
rations of  air  from  the  lungs  being  longer.  Children 
laugh  and  cry  in  the  same  breath. 

780  Why,  in  straining  to  lift  weights,  or  to  make  any  powerful  bodily 
effort,  do  we  compress  our  breath  ? 

We  shut  up  the  air  in  the  lungs  in  order  to  give 
increased  steadiness  and  firmness  to  the  body. 

781  When  is  a  person  suffocated? 

When  the  windpipe  becomes  choked,  or  the  supply  of 
air  to  the  lungs  is  in  any  way  cut  off. 

783   Why  do  birds  sing  comparatively  louder -than  man  f 

Because  the  strength  of  the  larynx,  and  of  the  muscles 
of  the  throat,  in  birds,  is  infinitely  greater  than  in  the 
human  race.  The  loudest  shout  of  man  is  but  a  feeble 
cry  compared  with  that  of  the  golden-eyed  duck,  the 
wild  goose,  or  even  the  woodlark. 

783  How  are  winged  insects  generally  found  to  produce  sound  f 

Generally  they  excite  sonorous  vibrations   by  the 


124:  SCIENCE   OF   COMMON   THINGS. 

Bounds  of  Insects.  Echoes.  "Where  echoes  occur. 

fluttering  of  their  wings  or  other  membranous  parts  of 
their  structure. 

7 84  How  do  locusts  produce  sound  f 

They  are  furnished  with  an  air-bladder,  or  a  species 
of  bagpipe,  placed  under  and  rather  behind  their  wings. 


CHAPTEE    III. 

KEFLECnON   OF   SOUNDS. 

785  What  is  an  echo  f 

An  echo  is  a  reflection  of  sound. 

786  Will  you  explain  the  manner  in  which  an  echo  is  produced  f 

When  a  wave  or  undulation  of  water  strikes  against 
a  smooth  surface,  it  is  reflected,  or  turned  back,  and 
waves  moving  in  an  opposite  direction  are  produced. 
The  same  thing  takes  place  with  a  sound-wave  of  air :  we 
hear  first  the  sound  proceeding  directly  from  the  sono- 
rous body ;  then,  if  the  sound-wave  strikes  against  a 
proper  surface,  at  a  suitable  distance,  it  is  turned  back, 
and  we  hear  a  repetition  of  the  sound.  This  repetition 
we  call  an  echo. 

787*  Are  echoes  often  Tieard  at  sea  or  on  extensive  plains  f 

Yery  rarely ;  at  sea  or  on  an  extensive  plain  there 
are  no  surfaces  to  reflect  sound.  It  sometimes  happens, 
however,  that  in  these  situations  the  clouds  reflect  sound. 

788  In  what  places  do  echoes  most  frequently  occur  f 

In  caverns,  large  halls,  valleys  and  mountainous 
passes,  the  windings  of  long  passages,  etc. 

789  Why  are  these  places  famous  for  echoes  ? 

Because  the  sound-waves  cannot  flow  freely  forward, 
but  continually  strike  against  opposing  surfaces,  and 
are  turned  back. 


SCIENCE  OF  COMMON  THING8.  125 

Ancient  fable  of  echo.  Distance  requisite  to  produce  echo. 

7*00  What  beautiful  fiction  existed  among  the  ancients  relative  to  the 
production  of  echo  f 

They. supposed  that  Echo  was  a  nymph  who  dwelt 
concealed  among  the  rocks,  and  who  repeated  the 
sounds  she  heard. 

791  At  what  distance  must  the  body  reflecting  the  sounds  be  situated  in 
order  to  produce  an  echo  f 

It  is  requisite  that  the  reflecting  body  should  be 
situated  at  such  a  distance  from  the  source  of  sound, 
that  the  interval  between  the  perception  of  the  original 
and  reflected  sounds  may  ~b&  sufficient  to  prevent  them 
from  being  blended  together. 

793  When  the  seunds  become  thus  blended  together,  what  is  the  effect 
called  ? 

A  resonance,  and  not  an  echo. 

793   Why  do  not  the  watts  of  a  room  of  ordinary  size,  produce  an  echo  f 

Because  the  reflecting  surface  is  so  near  the  source 
of  sound  that  the  echo  is  blended  with  the  original 
sound  /  and  the  two  produce  but  one  impression  on 
the  ear. 

7*94  Why  do  very  large  buildings  (as  cathedrals)  often  reverberate  the 
voice  of  the  speaker  ? 

Because  the  walls  are  so  far  off  from  the  speaker, 
that  the  echo  does  not  get  oack  in  time  to  blend  with 
the  original  sound ;  and  therefore  each  is  heard  sepa- 
rately. 

7*95   Why  do  some  echoes  repeal  only  one  syllable  ? 

Because  the  echoing  body  is  very  near.  The  farther 
the  echoing  body  is  oif,  the  more  sound  it  will  reflect  : 
if,  therefore,  it  be  very  near,  it  will  repeat  but  one  syl 
lable. 

790   Why  does  an  echo  sometimes  repeat  two  or  more  syllables  f 

Because  the  echoing  body  is  far  off ;  and  therefore 
there  is  time  for  one  reflection  to  pass  away  before  an- 
other reaches  the  ear. 

All  the  syllables  must  be  uttered  before  the  echo  of  the  first  syllable  \ 
reaches  the  ear :  if,  therefore,  a  person  repeats  7  syllables  in  2  seconds  of   \ 
time,  and  hears  them  all  echoed,  the  reflecting  object  is  1142  feet  distant  ; 
because  sound  travels  1142  feet  in  a  second,  and  the  words  take  one 
second  to  go  to  the  reflecting  object,  and  one  second  to  return. 

6* 


126  SCIENCE  OF  COMMON  THINGS. 

Effect  of  surfaces  on  sound.  Construction  of  halls  for  speaking. 

797  What  must  be  the  conditions  of  the  reflecting  surface  in  order  to 
produce  a  perfect  echo  ? 

The  surface  must  be  smooth  and  of  some  regular 
form ;  for  the  wave  of  sound  rebounds,  according  to 
the  same  law  as  a  wave  of  water  or  an  elastic  ball,  per- 
pendicularly to  the  surface  if  it  fall  perpendicularly, 
and  if  it  fall  obliquely^  on  one  side,  it  departs  with  an 
equal  degree  of  ooliquity  on  the  other  side. 

798  What  must  be  the  effect  of  an  irregular  surface  ? 

An  irregular  surface  must  break  the  echo  ;  and  if 
the  irregularity  be  very  considerable,  there  can  be  no 
distinct  or  audible  reflection  at  all.  For  this  reason  an 
echo  is  much  less  perfect  from  the  front  of  a  house 
which  has  windows  and  doors,  than  from  the  plane 
end,  or  any  plane  wall  of  the  same  magnitude. 

799  Why  have  halls  for  music  plane  bare  walls  f 

Because  the  hard  plane  walls  reflect  the  sound  regu- 
larly, and  increase  the  effect  of  the  music. 

800  Why  are  halls  for  speaking,   theatres,  churches,  etc.,  generally 
ornamented  on  the  wall,  and  furnished  with  pittars,  curtains,  etc. 

Because  the  ornaments ,  pillars,  curtains,  etc.,  form 
irregular  surfaces,  which  break  up  and  destroy  the 
echoes  and  resonances. 

801  Why  is  a  thick  curtain  often  placed  behind  a  pulpit  or  speaking- 
desk  f 

Because  the  material  absorbs  the  sound,  and  by  not 
reflecting  it  avoids  the  production  of  echoes  and  reso- 
nances. 

If  the  room  is  not  rery  large,  a  curtain  behind  the  speaker  impedes 
rather  than  assists  his  voice. 


SOS    What  is  a  speaking  trumpet  f 

A  speaking  trumpet  is  a  hollow  tube,,  so  constructed, 


SCIENCE  OF   COMMON   THINGS.  127 

Construction  of  the  speaking  trumpet.  Ear  trumpet. 

that  the  rays  of  sound  (proceeding  from  the  mouth 
when  applied  to  it),  instead  of  diverging,  and  being 
scattered  through  the  surrounding  atmosphere,  are 
reflected  from  the  sides,  and  conducted  forward  in 
straight  lines,  thus  giving  great  additional  strength  to 
i  the  voice.  The  course  of  the  rajs  of  sound  proceeding 


Fig.  33. 

from  the  mouth  through  this  instrument,  may  be  shown 
by  Fig.  33.  The  trumpet  being  directed  to  any  point* 
a  collection  of  parallel  rays  of  sound  moves  towards 
such  point,  and  they  reach  the  ear  in  much  greater 
number  than  would  the  diverging  rays  which  would 
proceed  from  a  speaker  without  such  an  instrument. 

8O3   What  is  an  ear  trumpet  f 

An  ear  trumpet,  Fig.  34,  is  in  form  and  application 
the  reverse  of  a  speaking  trumpet,  but 
in  principle  the  same.  The,  rays  of 
sound  proceeding  from  a  speaker,  more 
or  less  distant,  enter  the  hearing  trum- 
pet, and  are  reflected  in  such  a  manner 
as  to  concentrate  the  sound  upon  the 
opening  of  the  ear.  Fig.  34  repre- 
sents the  form  of  the  ear  trumpet  generally  used  by 
deaf  pei-sons.  The  aperture  A  is  placed  within  the  ear, 
and  the  sound  which  enters  at  B  is,  by  a  series  of 
reflections  from  the  interior  of  the  instrument,  concen- 
trated at  A. 

SO  ±  Why  do  persons  hold  the  hand  concave  behind  the  ear,  in  order  to 
hear  more  distinctly  ? 

Because  the  concave  hand  acts  in  some  respects  as 
an  ear  trumpet,  and  reflects  -the  sound  into  the  ear. 


128  SCIENCE   OF  COMMON  THINGS. 

Sound  lender  in  a  church  than  on  a  plain.  Haunted  bouses. 

805    Why  does  sound  seem  louder  in  a  church  or  hatt  than  on  a  plain  t 

Because  the  sides  of  the  building  confine  the  sound- 
waves, and  prevent  their  spreading  ;  in  consequence  of 
which  their  strength  is  greatly  increased. 

SOS  How  can  most  of  the  stories  in  respect  to  the  so-called  "haunted 
houses'11  be  explained  ? 

By  reference  to  the  principles  which  govern  the 
reflection  of  sounds.  Owing  to  a  peculiar  arrangement 
'of  reflecting  walls  and  partitions,  sounds  produced  by 
ordinary  causes  are  often  heard  in  certain  localities  at 
remote  distances,  in  apparently  the  most  unaccountable 
manner.  Ignorant  persons  become  alarmed,  and  their 
imagination  connects  the  phenomenon  with  some  super- 
natural cause. 


SCIENCE  OF  COMMON  THINGS.  129 

What  is  heat  and  heat  matter  ? 

PART  V. 

HEAT. 


CHAPTER   L 

NATURE   AND  ORIGIN   OF  HEAT. 
8O7  What  is  heat  f 

In  ordinary  language  the  term  heat  expresses  the 
sensation  of  warmth  which  we  experience  when  any 
portion  of  our  body  comes  in  contact  with  a  substance 
which  is  warmer  than  itself? 

SOS  Do  we  really  know  what  heat  is? 

We  do  not ;  we  only  know  and  study  the  effects 
which  it  produces  on  matter. 

SOS  To  what  cause  have  different  philosophers  attributed  the  phenomenon 
of  heat? 

Some  have  supposed  the  phenomenon  of  heat  to  be 
merely  a  species  of  motion  among  the  minute  particles 
of  bodies  generally,  as  sound  is  motion  of  another  kind 
among  the  same  particles  ;  others  have  supposed  that 
heat  arises  from  the  presence  of  a  pecuUa/r  fluid  or 
ethereal  kind  of  matter. 

S1O  Is  it  generally  believed  at  the  present  time  that  heat  is  a  material 
substance  ? 

It  was  believed  formerly  that  heat  was  a  kind  of 
matter ;  but  now  it  is  generally  considered  that  heat 
has  no  material  existence. 

811  What  great  fact  is  opposed  to  the  idea  that  heat  has  a  separate 
material  existence  as  a  fluid  ? 

The  fact  that  nature  nowhere  presents  us,  neither  has 
art  ever  succeeded  in  showing  us,  heat  alone  in  a  sepa- 
rate state. 


130  SCIENCE  OF   COMMON   THINGS. 

Heat  has  no  weight  How  heat  is  measured.  What  is  cold  ? 

SIS  Has  heat  any  perceptible  weight? 

No ;  if  we  balance  a  quantity  of  ice  in  a  delicate 
scale,  and  then  leave  it  to  melt,  the  equilibrium  will 
not  be  in  the  slightest  degree  disturbed.  If  we  substi- 
tute for  the  ice  boiling  water  or  a  red-hot  iron,  and  leave 
this  to  cool,  there  will  be  no  difference  in  the  result. 

813  What  important  property  distinguishes  heat  from  all  other  agents 
or  substances  in  nature  f 

The  property  of  passing  through  and  existing  in  all 
kinds  of  matter  at  ail  times  /  heat  is  everywhere  present, 
and  every  body  that  exists  contains  it  without  known 
limit. 

814  Has  ice  heat  ? 

Yes,  large  quantities  of  it.  Sir  Humphrey  -Davy,  by 
friction,  extracted  heat  from  two  pieces  of  ice,  and 
quickly  melted  them,  in  a  room  cooled  below  the  freez- 
ing point,  by  rubbing  them  against  each  other. 

815  How  do  we  measure  the  quantity  of  heat  in  different  bodies,  or  judge 
of  its  effects  ? 

Only  by  the  change  in  hulk  or  appearance  which 
different  bodies  assume,  according  as  neat  is  added  or 
subtracted. 

810  According  to  what  law  does  heat  diffuse  or  spread  itself 'f 

Heat  diffuses  or  spreads  itself  among  neighboring 
bodies  until  all  have  acquired  the  same  temperature  / 
that  is  to  say,  until  all  will  similarly  affect  the  thermo- 
meter. 

817*  Why  does  a  piece  of  iron  thrust  into  burning  coals  become  hoi 
among  them  f 

Because  the  heat  passes  from  the  coals  into  the  iron 
until  the  metal  has  acquired  an  equal  temperature. 

818   What  is  cold? 

Cold  is  a  relative  term  expressing  only  the  absence 
of  heat  in  a  degree ;  not  its  total  absence,  for  heat 
exists  always  in  all  bodies. 

810  When  the  hand  touches  a  body  having  a  higher  temperature  than 
itself,  why  do  we  call  it  hot  ? 

Because  on  account  of  the  law  that  heat   diffuses 


SCIENCE  OF  COMMON  THINGS.  131 

When  is  a  body  cold  f  What  is  fire  ?  Effects  of  heat. 

itself  among  neighboring  bodies  until  all  have  acquired 
the  same  temperature,  neat  passes  from  the  body  of 
higher  temperature  to  the  hand,  and  causes  a  peculiar 
sensation,  which  we  call  warmth. 

SSO   Under  what  circumstances  do  we  call  a  body  cold  f 

When  we  touch  a  body  having  a  temperature  lower 
than  that  of  the  hand,  heat,  in  accordance  with  the  above 
law,  passes  out  from  the  hand  to  the  body  touched,  and 
occasions  the  sensation  which  we  call  cold. 

831   What,  then,  really  are  the  sensations  of  heat  and  cold  f 

Merely  degrees  of  temperature,  contrasted  by  name 
in  reference  to  the  peculiar  temperature  of  the  indivi- 
dual speaking  of  them. 

833   When  is  a  body  said  to  be  incandescent  or  ignited  f 

When  the  body  naturally  incapable  of  emitting  light 
is  heated  to  sufficient  extent  to  become  luminous. 

833  What  is  flame? 

Flame  is  ignited  gas  issuing  from  a  burning  body. 

834  What  is  fire  f 

The  appearance  of  heat  and  light  in  conjunction,  pro- 
duced by  the  combustion  of  inflammable  substances. 

835  What  character  was  attributed  to  fire  by  the  ancient  philosophers  f 

They  used  the  term  fire  as  a  characteristic  of  the 
matter  of  heat,  and  regarded  it  as  one  of  the  four  ele- 
ments of  nature. 

83B  Enumerate  the  general  physical  properties  of  heat. 

It  is  invisible,  without  weight,  with  great  tendency 
to  diffuse  itself,  and  is  absorbed  by  all  bodies. 

837  What  are  the  principal  effects  of  heat  1 

Expansion,  liquefaction,  vaporization,  and  ignition. 

838  What  do  we  understand  by  the  term  caloric  f 

Caloric  is  a  name  often  used  to  indicate  the  agent 
which  produces  the  sensation  of  warmth;  since  the  term 
"  heat,"  as  generally  used,  refers  only  to  the  sensation. 

839  Is  caloric  equally  distributed  over  the  globe  f 

No  ;  at  the  equator  the  average  temperature  is 


132  SCIENCE   OF   COMMON   THINGS 

Sources  of  heat.  The  sun  a  source  of  heat.  Burning-glasses. 

while  at  the  poles  it  is  believed  to  be  about  13°  below 
zero. 

"  Average  temperature" — that  is,  the  mean  or  medium  temperature. 
"ZERO" — the  point  from  which  a  thermometer  is  graduated;  it  is  32' 
below  freezing,  Fahrenheit's  thermometer. 

83  O  How  many  sources  of  heat  are  recognised  to  exist  t 

Six. 

831  What  are  they  f 

1.  The  sun:  2.  The  interior  of  the  earth  •  3.  Electri- 
city ;  4^  Vital  action ;  5.  Mechanical  action  •  6.  Che- 
mical action. 


CHAPTEE    II 

THE   SUN   A   SOURCE   OF  HEAT- 
83S  What  is  the  great  natural  source  of  heat  f 

The  sun. 

833  Why  do  burning-glasses  set  fire  to  substances  submitted  to  their 
power? 

Because,  when  the  rays  of  the  sun 
pass  through  the  burning-glass,  they 
are  bent  towards   one  point,   called 
the^   "  focus ;"     in    consequence    of 
_         .  _         which  the   light  and    heat    at    this 
~Fi*™35.  point  are  very  greatly  increased. 

Fig.  35  represents  the  manner  in  which  a  burning-glass  concentrates 
or  bends  down  the  rays  of  heat  until  they  meet  in  a  focus. 

834  Do  the  rays  of  the  sun  ever  set  fire  to  natural  substances  without 
the  assistance  of  a  burning-glass  f 

No  ;  the  rays  of  the  sun,  even  in  the  torrid  zone,  are 
never  hot  enough  to  kindle  natural  substances,  unless 
concentrated  by  a  "burning-glass. 

835  Does  the  heat  of  the  sun  possess  any  different  properties  from  arti- 
ficial heat? 


SCIENCE   OF   COMMON  THINGS.  133 

Heat  of  the  sun.  Cause  of  spring,  summer,  and  winter. 

The  heat  of  the  sun  passes  readily  through  glass, 
whereas  this  property  is  possessed  by  artificial  heat  in 
a  very  small  degree. 

836  What  is  the  generally  received  opinion  at  present,  in  regard  to  the 
actual  temperature  of  the  visible  surface  of  the  sun  1 

That  the  temperature  of  its  luminous  coating  is  much 
more  elevated  than  any  artificial  heat  we  are  able  to 
produce. 

837  Why  is  the  heat  of  the  sun  always  greater  in  some  portions  of  the 
earth  than  at  others  ? 

Owing  to  the  position  of  the  earth's  axis,  the  rays  of 
the  sun  always  fall  more  directly  upon  the  central  por- 
tion of  the  earth  than  they  do  at  the  poles  or  extremities. 

838  Upon  what  does  the  succession  of  spring,  summer,  autumn,  and 
winter,  and  the  variations  of  temperature  of  the  seasons,  depend  ? 

Chiefly  upon  the  position  of  the  sun  in  relation  to  the 
earth. 

839  When  do  we  experience  the  greatest  amount  of  heat  from  the  rays 
of  the  sun  f 

When  its  rays  fall  most  perpendicularly. 

840  Why  is  the  heat  of  the  sun  greatest  at  noon  ? 

Because  for  the  day  the  sun  has  reached  the  highest 
point  in  the  heavens,  and  its  rays  fall  more  perpendicu- 
larly than  at  any  other  time. 

84:1   Why  is  it  warmer  in  summer  than  in  winter  f 

Because  in  summer  the  position  of  the  sun  is  such 
that  its  rays  fall  more  perpendicularly  than  at  any  other 
season.  The  sun  is  longer  above  the  horizon  in  summer 
than  in  winter,  and  consequently  imparts  the  greatest 
amount  of  heat. 

843   Why  is  it  colder  in  winter  than  in  summer  f 

Because  in  winter  the  position  of  the  sun  is  such  that 
its  rays  fall  more  obliquely  upon  the  earth  than  at  any 
other  season.  The  sun  is  also  for  a  less  time  above  the 
horizon  in  winter  than  in  summer,  and  consequently 
imparts  less  heat. 

843  Upon  what  does  the  heating  power  of  the  sun  depend  in  a  great 
measure  ? 


134  SCIENCE   OF  COMMON  THINGS. 

Effect  of  the  inclination  of  the  sun's  rays.  Natural  heat 

Upon  its  altitude  or  height  above  the  horizon  /  tlie 
greater  its  altitude,  the  more  perpendicularly  will  its 
rays  fall  upon  the  earth,  and  the  greater  their  heating 
effect ;  the  less  the  altitude,  the  more  obliquely  will  its 
rays  fall,  and  the  less  their  heating  effect. 

844  Why  should  the  difference  in  the  inclination  of  the  sun's  rays  fall- 
ing upon  the  earth  occasion  a  difference  in  their  heating  effect  f 

Because  the  more  the  rays  are  inclined,  the  larger 
the  space  over  which  they  fall. 

Let  us  suppose  A  B  C  D,  Fig.  36, 
to  represent  a  portion  of  the  sun's 
rays;  and  C  D  a  portion  of  the 
earth's  surface  upon  which  the  rays 
fall  perpendicularly,  and  C  F  and 
C  E  portions  of  the  surface  upon 
which  they  fall  obliquely.  Now, 

Fig.  36.  it  is  obvious  that  the  surfaces  C  F 

and  C  E  are  greater  than  the 
Burface  C  D ;  and  as  the  same  amount  of  rays  of  light  and  heat  fall  upon 
all  the  surfaces,  it  is  clear  that  they  will  fall  more  densely  upon  the 
smaller  surface  (i.e.  that  it  will  be  warmer  there)  and  more  diffusely 
over  the  inclined  or  oblique  surface  (where  it  will  be  colder). 

845  What  is  the  greatest  natural  heat  ever  observed  f 

On  the  west  coast  of  Africa  the  thermometer  (Fah- 
renheit) has  been  observed  as  high  as  108°  in  the 
shade  /  Burckhardt,  in  Egypt,  and  Humboldt,  in  South 
America,  observed  it  at  117°  F. ;  and,  in  181 9-,  at  Bag- 
dad, the  thermometer  rose  to  120°  F.  in  the  shade. 

840    What  is  the  lowest  atmospheric  temperature  ever  observed  f 

From  60°  to  70°  below  the  zero  of  Fahrenheit's  ther- 
mometer. This  temperature  has  been  observed  by  Dr. 
Kane  and  other  Arctic  navigators. 

84*7   What  is  the  greatest  artificial  cold  ever  produced  f 

220°  below  zero,  which  temperature  was  attained  by 
Prof.  Natterer.  At  this  temperature,  pure  alcohol  and 
ether  did  not  freeze. 

848  What  is  the  estimated  temperature  of  the  space  above  the  earth's 
atmosphere  ? 

58°  below  zero. 

849  At  what  temperature  does  mercury  freeze  T 


SCIENCE   OF   COMMON   THINGS.  135 

Extremes  of  temperature.       Melting  point  of  iron.         Greatest  artificial  heat. 

3S°-6  below  zero. 

850  At  what  temperature  does  fresh  water  freeze? 

At  32°  above  zero. 

851  At  what  temperature  does  salt  or  sea  water  freeze  f 

At  28° '5  above  zero. 

85S   Why  does  it  require  a  greater  amount  of  cold  to  cause  sea  water  to 
congeal,  than  it  does  fresh  water  f 

Because  sea  water  contains  salt  and  other  substances 
which  tend  to  prevent  congelation. 

853  What  is  the  average  temperature  at  the  equator  1 

In  America,  81°'5  ;  in  Africa^  83°. 

854  What  is  blood-heat,  or  the  vital  temperature  of  the  human  body  t 

98°. 

855  At  what  temperature  does  alcohol  boil  f 

Under  the  ordinary  atmospheric  pressure  at  1T3°*5. 

856  At  what  temperature  does  water  boil  T 

Under  the  ordinary  atmospheric  pressure  at  212°. 

85*7  At  what  temperature  does  lead  melt  ? 

At  594°. 

858  At  what  heat  does  mercury  boilf 

At  661°  under  the  common  atmospheric  pressure. 

859  At  ivhat  temperature  do  brass,  copper,  silver,  and  gold  melt  ? 

Brass  at  1869° ;  copper,  1996° ;  silver,  1873°  ;  gold, 
2016°. 

860  At  what  temperature  does  cast-iron  melt  ? 

At  2786°. 

861  What  is  the  greatest  degree  of  artificial  heat  which  we  have  been 
enabled  to  measure  f 

A  furnace  heat  of  3280°  :  at  this  heat  wrought  iron 
and  platinum  did  not  melt. 


136  SCIENCE   OF  COMMON   THINGS. 

Heat  of  the  earth.  Cause  of  earthquakes. 

CHAPTEE  III. 

OTHER   SOURCES   OF   HEAT   BESIDES   THE   SUN. 

862  How  far  below  the  surface  of  the  earth  does  the  influence  of  solar 
heat  extend  ? 

The  depth  varies  from  50  to  100  feet /  never,  how- 
ever, exceeding  the  latter  distance. 

863  How  do  we  know  that  the  earth  is  a  source  of  heal  f 

Because  we  find  as  we  descend  into  the  earth  and 
pass  beyond  the  limit  of  solar  heat,  that  the  tempera- 
ture constantly  increases. 

864  At  what  rate  does  the  temperature  increase  f 

About  one  degree  of  the  thermometer  for  every  fifty 
feet. 

865  Supposing  the  temperature  to  continue  to  increase  according  to  this 
ratio,  what  would  be  its  effects  at  different  deptJis  1 

At  the  depth  of  two  miles  water  would  be  converted 
into  steam ;  at  four  miles,  tin  would  be  melted ;  at 
five  miles,  leaa;  and  at  thirty  miles,  almost  every 
earthy  substance  would  be  reduced  to  a  fluid  state. 

866  To  what  cause  may  earthquakes  and  volcanoes  be  attributed  f 

Undoubtedly  to  the  agency  of  the  internal  haat  of 
the  earth. 

867  What  effect  has  the  internal  heat  of  the  earth  on  the  temperature 
of  the  surface  ? 

JVo  sensible  effect:  it  has  been  calculated  that  it 
affects  the  temperature  of  the  surface  less  than  ^V  of  a 
degree  of  the  thermometer. 

868  WAy,  if  so  great  an  amount  of  heat  exist  in  the  interior  of  the 
earth,  does  it  not  appear  more  manifest  upon  the  surface  f 

Because  the  materials  of  which  the  exterior  strata  or 
crust  of  the  earth  is  composed,  do  not  conduct  it  to  the 
surface  from  the  interior. 

869  In  what  manner  is  electricity  a  source  of  heat? 

When  an  electric  current  passes  from  one  substance 


SCIENCE  OF  COMMON  THINGS.  137 


Heat  of  electricity.  Heat  of  chemical  action. 

to  another,  the  substance  which  serves  to  conduct  it  is 
very  frequently  heated  ;  but  in  what  manner  the  heat 
is  produced,  we  have  no  positive  information. 

8  7O  How  great  a  degree  of  heat  is  electricity  capable  of  generating  f 

The  greatest  known  heat  with  which  we  are  acquaint- 
ed, is  produced  by  the  agency  of  the  electric  or  gal- 
vanic current.  Ah1  known  substances  can  be  melted  or 
volatilized  by  it. 

871  Has  the  heat  generated  by  electricity  been  employed  for  any  prac- 
tical or  economical  purposes  ? 

Not  to  any  great  extent ;  but  for  philosophical  experi- 
ments and  investigations  it  has  been  made  quite  useful. 

873   What  is  chemical  action  ? 

We  apply  the  term  chemical  action  to  those  opera- 
tions, whatever  they  may  be,  by  which  the  weight,  form, 
solidity,  color,  taste,  smell,  and  action  of  substances 
become  changed ;  so  that  new  bodies  with  quite  different 
properties  are  formed  from  the  old. 

873  How  does  chemical  action  become  a  source  of  heat  ? 

Many  bodies,  when  their  original  constitution  is 
altered,  either  by  the  abstraction  of  some  of  their  com- 
ponent parts,  or  by  the  addition  of  other  substances  not 
before  in  combination  with  them,  evolve  heat  while  the 
change  is  taking  place. 

874  Explain  by  illustration  what  you  mean. 

"Water  is  cold,  and  sulphuric  acid  is  cold ;  but  if  these 
two  cold  liquids  be  mixed  together,  they  will  produce 
intense  heat. 

875  Why  does  cold  water  poured  on  lime  make  it  intensely  hot  ? 

Because  heat  is  evolved  by  the  chemical  action  which 
takes  place  when  the  cold  water  combines  with  the  lirne. 

Heat  is  always  evolved  when  a  fluid  is  converted  into  a  solid  form. 
Heat  is  always  absorbed  when  a  solid  is  changed  into  a  liquid  state.  As 
the  water  is  changed  from  its  liquid  form  when  it  is  taken  up  by  the  lime, 
therefore  heat  is  given  off. 

87Q   Where  does  the  heat  come  from  f 

It  was  in  the  water  and  lime  before,  but  was  in  a 
latent  state. 


138  SCIENCE   OF   COMMON   THINGS. 

Heat  in  all  bodies.  What  is  latent  heat?  Heat  in  ice. 

8*77*    Was  there  heat  in  Hie  cold  water  and  lime  before  they  were  mixed 
together  f 

Yes.     All  bodies  contain  heat. 

878  Is  there  heat  even  in  icef 

Yes ;  but  it  is  latent  (i.e.  not  perceptible  to  our 
senses). 

Latent,  from  the  Latin  word  lateo  (to  lie  hid). 
87*9  Does  cold  iron  contain  heat  ? 

Yes ;  everything  contains  heat ;  but  when  a  thing 
feels  cold,  its  heat  is  latent. 

88O   What  is  meant  by  latent  heat  ? 

Heat  not  perceptible  to  our  feelings.  "When  anything 
contains  heat  without  feeling  the  hotter  for  it,  that  heat 
is  called  u  latent  heat. 

S81  Does  cold  iron  contain  latent  heat  f 

Yes  ;  and  when  a  blacksmith  compresses  the  particles 
of  iron  by  his  hammer,  he  brings  out  latent  heat ;  and 
this  makes  the  iron  red  hot. 

382  Why  is  the  air  in  the  spring,  when  the  ice  and  snow  are  melting, 
always  very  chilly  and  cold  1 

Solid  bodies,  in  passing  to  the  liquid  state,  absorb  heat 
in  large  quantities ;  when  ice  and  snow  are  thawing, 
they  absorb  heat  from  the  air,  in  consequence  of  which 
its  temperature  is  greatly  reduced. 

883  Why  does  the  weather  always  moderate  on  the  fall  of  snow  t 

Bodies,  in  passing  from  the  liquid  to  the  solid  state, 
give  out  heat  y  snow  is  frozen  water,  and  in  its  forma- 
tion heat  is  imparted  to  the  atmosphere,  and  its  tem- 
perature increased. 

884  Why  does  the  temperature  of  melting  ice  and  snow  never  exceed 
32°? 

Because  all  the  heat  imparted  to  melting  ice  and 
snow  becomes  insensible,  until  the  liquefaction  is  com- 
plete. 

885  Can  we  be  made  to  feel  the  heat  of  ice  or  snow  f 

Yes.  Into  a  pint  of  snow  put  half  as  much  salt ; 
then  plunge  your  hands  into  the  liquid  ;  and  it  will  feel 
so  intensely  cold  that  the  snow  itself  will  seem  warm  in 
comparison  to  it. 


SCIENCE   OF   COMMON   THINGS.  139 

Salt  and  snow  produce  intense  cold — reason  of. 

886  Are  salt  and  snow  really  colder  than  snow  ? 

Yes,  many  degrees  ;  and  by  dipping  your  hand  into 
the  mixture  first,  and  into  snow  afterwards,  the  snow 
will  seem  to  be  comparatively  warm. 

887  Why  do  salt  and  snow  mixed  together  produce  intense  cold  ? 

The  salt  and '  snow  are  both  solids ;  when  they  are 
mixed,  the  salt  causes  the  snow  to  melt  by  reason  of  its 
attraction  for  water,  and  the  water  formed  dissolves 
the  salt :  so  that  both  pass  from  the  solid  to  the  liquid 
condition,  and  a  large  quantity  of  heat  is  absorbed. 
As  this  heat  is  derived  from  that  which  previously  ex- 
isted in  the  solids  themselves  in  a  sensible  state,  its 
abstraction  occasions  a  reduction  of  temperature. 

888  How  is  heal  produced  by  mechanical  action  f 

1.  By  percussion /  2.  By  friction  /  and  3.  By  con- 
densation. 

88Q   What  is  meant  by  percussion  f 

The  shock  produced  by  the  collision  of  two  bodies  ; 
as  when  a  blacksmith  strikes  a  piece  of  iron  on  his 
anvil  with  his  hammer. 

00 O  Why  does  striking  iron  make  it  red  hot  f 

Because  it  condenses  the  particles  of  the  metal,  and 
makes  the  latent  heat  sensible. 

801  What  is  meant  by  friction  f 

The  act  of  rubbing  two  things  together,  as  the  Indians 
rub  two  pieces  of  wood  together  to  produce  fire. 

80S  How  do  savages  produce  fire  by  merely  rubbing  two  pieces  of  dry 
wood  together  ? 

They  take  a  piece  of  dry  wood,  sharpened  to  a  point, 
which  they  rub  quickly  up  and  down  &  flat  piece  till  a 
groove  is  made ;  and  the  dust  (collected, in  this  groove) 
catches  fire. 

80S   Why  does  the  dust  of  the  wood  catch  fire  by  rubbing  f 

Because  latent  heat  is  developed  from  the  wood  by 
friction. 

804  Do  not  carnage  wheels  sometimes  catch  fire  f 

Yes  ;  when  the  wheels  are  dry,  or  fit  too  tightly,  or 
revolve  very  rapidly. 


140  SCIENCE   OF   COMMON   THINGS. 

Heat  caused  by  friction.  Use  of  greasing  cart  •wheels. 


Fig.  ST. 

Fig.  37  represents  an  Indian  explaining  the  method  of  kindling  a  fire 
by  the  friction  of  two  pieces  of  wood. 

895  Why  do  wheels  catch  fire  in  such  cases  ? 

Because  the  friction  of  the  wheels  against  the  axle- 
tree  disturbs  their  latent  heat,  and  produces  ignition. 

896  What  is  the  use  of  greasing  cart  wheels  f 

Grease  lessens  the  friction  ;  and,  because  there  is  less 
friction,  the  latent  heat  of  the  wheels  is  less  disturbed. 

89*7  Does  a  body  ever  cease  to  give  out  heat  by  friction  f 

No  j  however  long  the  operation  may  be  continued. 

898  What  conclusions  respecting  the  nature  of  heat  have  philosophers 
drawn  from  this  fact  ?  • 

That  heat  cannot  be  a  material  substance,  but  merely 
&  property  of  matter. 

899  Why  is  it  easier  to  produce  heat  from  the  friction  of  rough  sur- 
faces than  smooth  ones  f 

Because  in  the  friction  of  rough  surfaces  certain  par- 
ticles are  rubbed  off,  which,  being  small,  are  readily  con- 
densed, and  made  to  evolve  their  latent  caloric. 

900  Why,  when  you  rub  a  smooth  metallic  surface,  as  a  button,  for 
example,  against  apiece  qf  plank,  does  the  metal  become  more  heated  than  the 
wood? 

Because  the  caloric  is  forced  out  of  the  wood,  as  it 


SCIENCE   OF   COMMON   THINGS. 


How  a  friction  match  ignites.  Temperature  of  living  animals. 

were,  by  the  compression  of  its  parts,  and  the  button 
receives  most  of  the  caloric,  owing  to  a  stronger  attrac- 
tion for  it,  than  is  possessed  by  the  wood. 

9O1  Why  does  a  friction  match,  drawn  over  sandpaper  or  other  rough 
tubstance,  ignite  1 

When  the  match  is  drawn  over  sand  paper,  or  other 
rough  substance,  certain  phosphoric  particles  are  rub- 
bed off,  and  being  compressed  between  the  match  and 
the  paper,  their  heat  is  raised  sufficiently  high  to  ignite 
them,  and  fire  the  match.  If  the  match  be  drawn  over 
a  smooth  surface,  the  compression  must  be  increased,  for 
the  temperature  of  the  whole  phosphoric  mass  must  be 
raised  in  order  to  cause  ignition. 

0O3   What  singular  property  have  most  living  animal  bodies  f 

The  property  of  maintaining  in  themselves  an  equable 
temperature,  whether  surrounded  by  bodies  that  are 
hotter  or  colder  than  they  are  themselves. 

9O3  Illustrate  this  fact. 

The  sailors  of  the  Arctic  exploring  expedition  during 
the  polar  winter,  while  breathing  air  that  froze  mer- 
cury, still  had  in  them  the  natural  warmth  of  98°  Fah- 
renheit above  zero  ;  and  the  inhabitants  of  India,  where 
the  same  thermometer  sometimes  stands  115°  in  the 
shade,  have  their  blood  at  no  higher  temperature. 

SO  4  Do  vegetables  possess  in  any  degree  this  property  of  maintaiitkiy 
a  constant  temperature  within  their  structure  ? 

Growing  or  fresh  vegetables  have  this  property  to  a 
certain  extent. 

9O5    What,  then,  is  vital  heat? 

^  The  heat  generated  or  excited  by  the  organs  of  a 
living  structure. 

©O6    What  is  the  cause  of  vital  or  animal  heat? 

The  cause  of  animal  heat  is  not  certainly  known  or 
determined;  it  is  supposed  to  be  due  to  chemical 
action,  the  result  of  respiration  and  nervous  excitation. 

907  Has  {he,  power  of  animals  to  preserve  a  peculiar  temperature  any 
limits  ? 

Yes  ;  intense  cold  suddenly  coming  upon   a    man 
7 


14:2  SCIENCE   OF  COMMON   THINGS. 

Vital  heat.  Effect  of  climate  on  animals. 

who  has  not  sufficient  protection,  first  causes  a  sensation 
of  pain,  and  then  brings  on  an  almost  irresistible  sleepi- 
ness, which  if  indulged  in  proves  fatal.  A  great  excess 
of  heat  also  cannot  long  be  sustained  by  the  human 
system. 

©OS  Does  each  species  of  animal  appear  to  have  a  peculiar  tempera- 
ture? 

Yes ;  each  species  of  animal  and  vegetable  appears 
to  have  a  temperature  natural  and  peculiar  to  itself, 
and  from  this  diversity  different  races  are  fitted  for 
different  portions  of  the  earth's  surface. 

©O9  What  effect  does  the  peculiarity  of  temperature  have  upon  the  dis- 
tribution and  location  of  animals  and  plants  upon  the  earth's  surface  ? 

The  different  species  are  confined  and  circumscribed 
within  certain  districts,  depending  mainly  on  their  re- 
lations to  heat.  Thus,  the  orange-tree  and  the  bird  of 
Paradise  are  confined  to  warm  latitudes  ;  the  pine-tree 
and  the  Arctic  bear,  to  those  which  are  colder. 

01O  What  curious  fact  in  relation  to  a  species  of  whale  illustrates  the 
influence  of  temperature  in  defining  locations  ? 

It  has  been  ascertained  that  at  least  one  species  of 
whale  is  precluded  from  migrating  from  the  north  to 
the  south,  from  its  inability  to  live  in  the  heated  waters 
of  the  equator. 

©11  When  animals  or  plants  are  removed  from  their  peculiar  and 
natural  districts  to  one  entirely  different,  what  changes  take  place  f 

They  either  cease  to  exist,  or  change  their  character 
in  such  a  way  as  to  adapt  themselves  to  the  climate. 

913    What  curious  illustrations  do  we  find  of  this  f 

The  wool  of  the  northern  sheep  changes  in  the  tropics 
to  a  species  of  hair.  The  dog  of  the  torrid  zone  is 
nearly  destitute  of  hair.  Bees  transported  from  the 
north  to  the  region  of  perpetual  summer  cease  to  lay  up 
stores  of  honey ^  and  lose  in  a  great  measure  their  habits 
of  industry. 

©IS  How  has  nature  provided  for  the  protection  of  animals  against  the 
modifications  of  temperature  ? 

By  covering  their  bodies  with  &form  of  for.  or  hair, 
or  feathers,  in  the  exact  degree  required,  and  to  such 


SCIENCE   OF   COMMON   THINGS  143 

Man  only  lives  in  all  climates.  Communication  of  heat. 

an  extent  as  to  vary  the  covering  in  the  same  animal 
according  to  the  climate  and  season. 

914   What  one  species  of  organized  beings  is  fitted  to  live  in  all  climates  ? 

jbfan  alone  is  capable  of  living  in  all  climates,  and  of 
migrating  freely  to  all  portions  of  the  earth. 


CHAPTER   IY. 

HOW    HEAT    IS    COMMUNICATED. 

915  In  what  three  ways  may  heat  le  communicated  ? 

By  direct  contact,  by  conduction  and  convection, 
by  radiation. 

916  How  may  heat  be  communicated  by  contact  f 

"When  a  hot  body  touches  a  cold  one,  the  heat  passes 
directly  from  one  into  the  other,  as  when  it  enters  a  bar 
of  iron  put  into  the  fire,  or  the  hand  immersed  in  hot 
water. 

917*   When  is  heat  communicated  by  conduction  f 

When  the  heat  travels  from  particle  to  particle  of 
the  substance,  as  from  the  end  of  the  iron  bar  placed 
in  the  fire  to  that  part  of  the  bar  most  remote  from  the 
fire. 

91S    When  is  heat  communicated  by  radiation  f 

"When  the  heat  leaps,  as  it  were,  from  a  hot  to  a  cold 
body  through  an  appreciable  interval  of 'space,  as  when 
a  body  is  warmed  by  placing  it  before  a  fire  removed 
to  a  little  distance  from  it. 

919  In  ivhat  way  does  a  heated  body  cool  itself? 

first,  by  giving  off  heat  from  its  surface,  either  by 
contact  or  radiation,  or  both  conjointly  /  and,  secondly, 
by  the  heat  in  its  interior  passing  from  particle  to  par- 
ticle by  conduction  through  its  substance  to  the  surface. 


SCIENCE  OF   COMMON   THINGS. 


How  a  cold  body  is  heated.  Good  and  bad  conductors  of  heat. 

930  In  what  manner  does  a  cold  body  become  heated  ? 

First,  by  heat  passing  into  its  surface  either  by  con- 
tact or  radiation,  or  by  both  conjointly  j  and,  secondly  ^ 
by  tbe  heat  at  its  surface  passing  from  particle  to  par- 
ticle through  its  interior  portions  by  conduction. 

931  Does  heat  pass  through  all  bodies  with  tlie  same  velocity  ? 

No  ;  some  substances  oppose  very  little  impediment 
to  its  passage,  while  through  others  it  is  transmitted 
slowly. 

933  Into  what  two  classes  are  bodies  divided  in  respect  to  their  conduc- 
tion of  heat  ? 

Into  conductors  and  non-conductors  /  the  former  are 
such  as  allow  heat  to  pass  freely  through  them  ;  the 
latter  comprise  those  which  do  not  give  an  easy  pas- 
sage to  it. 

933  What  are  the  best  conductors  of  heat  f 

Dense,  solid  bodies,  such  as  metals,  glass,  some  varie- 
ties of  stone,  etc. 

934  What  are  the  worst  conductors  of  heat  ? 

All  light  and  porous  bodies  ;  such  as  hair,  fur,  wool, 
charcoal,  and  so  on. 

935  Why  do  some  things  feel  colder  than  otliers  f 

Principally  because  they  are  better  conductors,  and 
draw  off  heat  from  our  body  much  faster. 

936  Why  does  a  piece  of  wood  blazing  at  one  end  not  feel  hot  at  the 
other  f 

Because  wood  is  so  bad  a  conductor  that  heat  does 
not  traverse  freely  through  it  ;  hence,  though  one  end 
of  a  stick  be  blazing,  the  other  end  may  be  quite  cold. 

937  Why  does  hot  metal  feel  more  intensely  warm  than  hot  wool  ? 

Because  metal  gives  out  a  much  greater  quantity  of 
heat  in  the  same  space  of  time  •  and  the  influx  of  heat 
is,  consequently,  more  perceptible. 

933  Why  does  a  poJcer,  resting  on  a  fender,  feel  colder  than  the  hearth- 
rug, which  is  farther  off  from  the  fire  ? 

Because  the  poker  is  an  excellent  conductor,  and 
draws  heat  from  the  hand  much  more  rapidly  than  the 
woollen  hearth  rug,  which  is  a  very  bad  conductor  : 


SCIENCE   OF   COMMON"   THINGS.  145 

Familiar  illustrations  of  the  conduction  of'heat. 

though  both,  therefore,  are  equally  warm,  the  poker 
seems  to  be  the  colder. 

030  Why  does  a  stone  or  marble  hearth  feel  to  the  feet  colder  than  a  car- 
pet or  hearth-rug  ? 

Because  stone  and  marble  are  good  conductors  ;  but 
woollen  carpets  and  hearth-rugs  are  very  ~bad  conduc- 
tors. 

i      03O    Why  does  the  stone  hearth  make  our  feet  cold  f 

As  soon  as  the  hearthstone  has  absorbed  a  portion 
of  heat  from  our  feet,  it  instantly  disposes  of  it,  and 
calls  for  ^  fresh  supply ;  till  the  hearthstone  has  be- 
come of  the  same  temperature  as  the  foot  placed  upon  it. 

031  Do  not  also  the  woollen  carpet  and  hearth-rug  conduct  heat  from 
the  human  body  f 

Yes ;  but  being  very  lad  conductors,  they  convey 
the  heat  away  so  slowly  that  the  loss  is  scarcely  per- 
ceptible. 

©33  Is  the  cold  heartJistone  in  reality  of  the  same  temperature  as  the 
warm  carpet  f 

Yes ;  everything  in  the  room,  except  our  bodies,  is 
really  of  one  temperature  /  but  some  tilings  feel  colde* 
than  others,  because  they  are  letter  conductors. 

033  How  long  will  the  heartJistone  feel  cold  to  the  feet  resting  on  it  ? 

Till  iliefeet  and  the  hearthstone  are  bot/i  of  the  same, 
temperature  •  and  then  the  sensation  of  cold  in  the 
hearthstone  will  go  off. 

034  Why  would  not  the  hearthstone  feel  cold,  when  it  is  of  the  samf 
temperature  as  our  feet  ? 

Because  the  heat  would  no  longer  rush  out  of  ou1 
feet  into  the  hearthstone,  in  order  to  produce  equi' 
librium. 

035  Why  are  cooking  vessels  of  ten  furnished  with  wooden  handles? 

Because  wood  is  not  a  good  conductor  like  metal; 
and  therefore  wooden  handles  prevent  the  heat  of  the 
vessel  from  rushing  into  our  hands  to  burn  them. 

©36   Why  do  persons  use  paper  or  woollen  kettle-holders  f 

Because  paper  and  woollen  are  both  very  lad  con- 
ductors of  heat,  in  consequence  of  which  the  heat  of 


146  SCIENCE   OF   COMMON   THINGS. 

Conducting  power  of  water.  Stoves  and  furnaces. 

the  kettle  does  not  readily  pass  through  them  to  the 
hand. 

©37  Does  the  heat  of  the  boiling  kettle  never  get  through  the  woollen  or 
paper  kettle-liolder  f 

Yes ;  but  though  the  kettle-holder  became  as  hot  as 
the  kettle  itself,  it  would  never  feel  so  hot. 

038  Why  would  not  the  kettle-holder  feel  so  hot  as  the  kettle,  when  loth 
are  of  the  same  temperature. 

Because  it  is  a  very  lad  conductor,  and  disposes  of 
its  heat  too  slowly  to  be  perceptible  ;  but  metal  (being 
an  excellent  conductor)  disposes  of  its  heat  so  quickly, 
that  the  sudden  influx  is  painful. 

039  When  we  plunge  our  hands  into  a  basin  of  water,  why  does  it  pro- 
duce a  sensation  of  cold  f 

Because  water  is  a  better  conductor  than  air  ;  and,  as 
it  draws  off  the  heat  from  our  hands  more  rapidly,  it 
feels  colder. 

040  Why  does  the  conducting  power  of  water  make  it  feel  colder  than 
air? 

Because  it  abstracts  heat  from  our  hands  so  rapidly 
that  we  feel  its  loss ;  but  the  air  abstracts  heat  so  very 
slowly  that  its  gradual  loss  is  hardly  perceptible. 

041  Is  water  a  good  conductor  of  heat  ? 

No  ;  no  liquid  is  a  good  conductor  of  heat ;  but  yet 
water  is  a  much  better  conductor  than  air. 

04S    Why  is  water  a  bettei*  conductor  of  heat  than  air  1 

Because  it  is  more  dense  /  and  the  conducting  power 
of  any  substance  depends  upon  its  solidity,  or  the  close- 
ness of  its  particles. 

043  How  do  you  know  that  water  is  not  a  good  conductor  of  heat  ? 

Because  it  may  be  made  to  boil  at  its  surface,  without 
imparting  sufficient  heat  to  melt  ice  a  short  distance 
below  the  surface. 

044  Why  are  not  liquors  good  conductors  of  heat  f 

Because  the  heat  (which  should  be  transmitted)  pro- 
duces evaporation,  and  flies  off  in  the  vapor. 

045  //  air  is  not  a  good  conductor,  how  can  we  make  use  of  it  in 
warming  our  houses  by  means  of  stoves  and  furnaces? 


SCIENCE   OF   COMMON  THINGS.  147 

What  renders  clothing  necessary  ?  Use  of  woollens  and  furs. 


In  the  case  of  a  stove  or  furnace,  the  air  which  is  in 
contact  with  the  tire  or  the  heated  surface,  first  becomes 
heated,  expands,  and  rises  ;  cold  air  rushes  in  to  supply 
its  place,  is  heated,  and  ascends  in  like  manner,  and 
this  interchange  goes  on  until  all  the  air  in  the  room  is 
heated. 

946  If  air  be  a  bad  conductor  of  heat,  why  should  we  not  feel  as  warm 
without  clothing  as  when  we  are  wrapped  in  wool  and  fur  f 

Because  the  air  (which  is  cooler  than  our  body)  is 
never  at  rest  j  and  every  fresh  particle  of  air  draws  off 
a  fresh  portion  of  heat. 

947*  How  does  the  ceaseless  change  of  air  tend  to  decrease  the  warmth 
of  that  part  of  the  body  devoid  of  clothing  ? 

Thus :  the  air  (which  cases  the  body)  absorbs  as 
much  heat  as  it  can  while  it  remains  in  contact ;  being 
then  blown  away,  it  makes  room  for  a  fresh  coat  of 
air,  which  absorbs  more  heat. 

948  Does  the  air  which  encases  a  body  devoid  of  clothing  become  (by 
contact)  as  warm  as  the  body  itself? 

It  would  do  so  if  it  remained  motionless ;  but  as  it 
remains  only  a  very  short  time,  it  absorbs  as  much  heat 
as  it  can  in  the  time,  and  passes  on. 

949  Why  do  we  feel  colder  in  windy  weather  than  in  a  calm  day  f 

Because  the  particles  of  air  pass  over  us  more  rapidly, 
und  every  fresh  particle  takes  from  us  some  portion  of 
heat. 

950  Why  are  woollens  and  furs  used  for  clothing  in  cold  weather? 

Because  they  are  very  bad  conductors  of  heat ;  and 
therefore  prevent  the  warmth  of  the  body  from  being 
drawn  off  by  the  cold  air. 

951  Do  not  woollens  and  furs  actually  impart  heat  to  the  body  f 

No  ;  they  merely  prevent  the  heat  of  the  body  from 
escaping. 

953  Where  would  the  heat  escape  to,  if  the  body  icere  not  wrapped  in 
wool  or  fur  1 

The  heat  of  the  body  would  fly  off  into  the  air  ;  for 
the  cold  air  (coming  in  contact  with  our  body)  would 


148  SCIENCE   OF   COMMON    THINGS. 

Why  wool,  hair,  and  feathers  are  warm.  Icehouses. 

gradually  draw  away  its  heat,  till  it  was  as  cold  as  the 
air  itself. 

953  What,  then,  is  the  principal  use  of  clothing  in  winter-time? 

1.  To  prevent  the  animal  heat  from  escaping  too 
freely  ;  and 

2.  To  protect  the  body  from  the  external  air  (or  wind), 
which  would  carry  away  its  heat  too  rapidly. 

954  Why  are  ivool,  fur,  hair,  and  feathers  such  slow  conductors  of  heat  f 

Because  a  great  quantity  of  air  lurks  entangled 
between  the  fibres  ;  and  air  is  a  very  bad  conductor  of 
heat. 

The  warmest  clothing  is  that  which  fits  the  body  rather  loosely,  because 
more  hot  air  will  be  confined  by  a  moderately  loose  garment  than  by  one 
which  fits  the  body  tightly. 

955  How  are  whales,seals,  and  other  iv  arm-blooded  animals  that  live  in 
the  water  protected  against  the  cold  f 

They  are  enveloped,  beneath  the  sJcin,  with  a  thick 
coating  of  "  blubber"  or  fat,  which,  like  fur,  hair,  and 
feathers,  is  a  non-conductor  of  heat,  and  serves  to  pro- 
tect them  in  like  manner. 

95G  Why  are  blankets  and  warm  woollen  goods  always  made  with  a 
nap  cr  projection  of  fibres  on  the  outside  ? 

Because  the  nap  or  fibres  retain  air  among  them, 
which,  from  its  non-conducting  properties,  serves  to 
increase  the  warmth  of  the  material. 


How  does  the  covering  of  hair,  wool,  and  feathers  serve  to  keep  ani- 
mals cool  in  hot  weatlier,  as  well  as  warm  in  cool  weather  ? 

In  warm  w^eather  the  non-conducting  medium  will 
not  allow  the  heat  to  enter  the  \to&y  from  without  :  in 
cold  weather  the  heat  of  the  body  cannot  escape  from 
within. 

958  Why  do  we  wrap  up  ice  in  flannel  to  Jceep  it  from  melting  f 

Because  the  flannel,  being  a  non-conductor,  does  not 
allow  the  heat  of  the  atmosphere  to  penetrate  to  the  ice. 

959  In  the  construction  of  icehouses,  why  do  we  line  the  walls  and  roof 
with  straw  or  sawdust  % 

Because  these  substances  are  bad  conductors  of  heat, 

960  Why  is  it  good  economy  to  furnish  our  houses  in  winter  with  double 
windows  t 


SCIENCE   OF  COMMON  THINGS.  149 

Linen  cooler  than  cotton.  Influence  of  heat  on  the  soil. 

The  air  confined  between  the  two  surfaces  of  glass  is 
a  non-conductor  of  heat,  and  equally  opposes  the  escape 
of  caloric  from  within,  or  the  penetration  of  cold  air 
from  without. 

©61  Why  does  a  linen  garment  feel  colder  than  a  cotton  one? 

Because  linen  is  a  much  better  conductor  than  cotton ; 
and  therefore  (as  soon  as  it  touches  the  body)  it  draws 
away  the  heat  more  rapidly,  and  produces  a  greater 
sensation  of  cold. 

©6S  Why  is  the  face  cooled  by  wiping  the  temples  with  a  fine  cambric 
handkerchief^ 

Because  the  fine  fibres  of  the  cambric  have  a  strong 
capillary  attraction  for  moisture,  and  are  excellent  con- 
ductors of  heat ;  in  consequence  of  which  the  moisture 
and  heat  are  abstracted  from  the  face  by  the  cambric, 
and  a  sensation  of  coolness  produced. 

©63  Why  would  not  a  cotton  handkerchief  do  as  well  ? 

Because  the  coarse  fibres  of  cotton  have  less  capillary 
attraction,  and  are  very  bad  conductors;  in  conse- 
quence of  which  the  heat  of  the  face  would  be  increased 
(rather  than  diminished^  by  the  use  of  a  cotton  hand- 
kerchief. 

©64  Is  the  soil  a  good  conductor  of  heat  f 

]Nro ;  it  is  a  very  "bad  conductor  of  heat. 

©65  Why  is  the  soil  a  bad  conductor  of  heat  ? 

Because  its  particles  are  not  continuous;  and  the 
power  of  conducting  heat  depends  upon  the  density  of 
matter. 

966  Why  is  the  soil  (below  the  surface)  warmer  in  winter  than  the  sur- 
face itself? 

Because  it  is  a  ~bad  conductor  of  heat ;  and  therefore 
(although  the  ground  be  frozen)  the  frost  rarely  pene* 
trates  more  than  a  few  inches  below  the  surface. 

967*  Why  is  the  soil  (below  the  surface)  cooler  in  summer  than  the  sur- 
face itself 'f 

Because  it  is  a  bad  conductor  of  heat ;  and  therefore 
(although  the  surface  be  scorched  with  the  burning  sun) 

7* 


150  SCIENCE   OF   COMMON   THINGS. 


Coolness  of  spring  water.  Snow  protects  the  soil  from  cold. 


the  intense  heat  cannot  penetrate  to  the  roots  of  the 
plants  and  trees. 

908  Show  the  wisdom  of  the  Creator  in  making  the  soil  a  bad  con- 
ductor. 

If  the  heat  and  cold  could  penetrate  the  soil  deeply 
(as  freely  as  the  heat  of  a  fire  penetrates  iron),  the 
springs  would  be  dried  up  in  summer  and  frozen  in 
winter ;  and  all  vegetation  would  perish. 

909  Why  is  water  from  a  spring  always  cool,  even  in  summer  f 

Because  the  soil  is  so  bad  a  conductor,  that  the  burn- 
ing rays  of  the  sun  can  penetrate  only  a  few  inches  below 
the  surface ;  in  consequence  of  which  the  springs  of 
water  are  not  affected  by  the  heat  of  summer. 

97*O  How  does  the  non-conducting  power  of  snow  protect  vegetabks  from 
the  frost  and  cold  f 

It  prevents  the  heat  of  the  soil  from  being  drawn  off 
by  the  cold  air  which  rests  upon  it. 

97*1   Why  is  snow  a  non-conductor  of  heat  ? 

Principally  because  it  contains  a  large  quantity  of 
air  between  its  particles. 

97*3    Why  is  it  cool  under  a  shady  tree  in  a  hot  summer's  day  ? 

1.  Because  the  overhanging  foliage  screens  off  the 
rays  of  the  sun  / 

2.  As  the  rays  of  the  sun  are  warded  off,  the  cir 
(beneath  the  tree)  is  not  heated  by  the  reflection  of  the 
soil;  and 

3.  The  leaves  of  the   trees,   being  non-conductors, 
also  obstruct  the  transmission  of  heat. 

97*3  Why  does  a  metal  spoon  (left  in  a  kettle)  retard  the  process  of 
boiling  f 

Because  the  metal  spoon  (being  an  excellent  con- 
ductor) carries  off  the  heat  from  the  water ,  and  (as 
heat  is  carried  off  by  the  spoon)  the  water  takes  a 
longer  time  to  boil. 

97*4    Why  does  paint  preserve  wood  f 

1.  Because  it  covers  the  surface  of  the  wood,  and 
prevents  both  air  and  damp  from  penetrating  into  the 
pores ; 


SCIENCE   OF   COMMON   THINGS.  151 

Cellars,  why  warm  in  winter  and  cool  in  summer. 

2.  Because  paint    (especially  white  paint),  being  a 
bad  conductor,  preserves  tlie  wood  of  a  more  uniform 
temperature ;  and 

3.  Because  it  fills  up  the  pores  of  the  wood,  and  pre- 
vents insects  and  vermin  from  harboring  therein  and 
eating  up  the  fibre. 

97*5  Why  are  furnaces  and  stoves  (inhere  much  heat  is  required)  built 
of  porous  bricks  f 

Because  bricks  are  bad  conductors,  and  prevent  the 
escape  of  heat /  in  consequence  of  which  they  are  em?- 
ployed  where  great  heat  is  required. 

0*76    Why  do  cellars  feel  warm  in  winter  1 

Because  the  external  air  has  not  free  access  into  them1 5 
in  consequence  of  which  they  remain  almost  at  an  even 
temperature,  which  (in  winter-time)  is  about  10  degrees 
warmer  than  the  external  air. 

97*7*   Why  do  cellars  fed  cold  in  summer  f 

Because  the  external  air  has  not  free  access  into  them ; 
in  consequence  of  which  they  remain  almost  at  an  even 
temperature,  which  (in  summer-time)  is  about  10  de- 
grees colder  than  the  external  air. 

97*8    Why  do  the  Laplanders  wear  skins  with  the  fur  imvardsf 

Because  the  dry  skin  prevents  the  wind  from  pene- 
trating to  their  body ;  and  the  air  (between  the  hairs 
of  the  fur)  soon  becomes  heated  by  the  body  /  in  conse- 
quence of  which  the  Laplander  in  his  fur  is  clad  in  a 
case  of  hot  air,  impervious  to  the  cold  and  wind. 

97*9  In  what  respect  is  bark  especially  adapted  as  a  covering  for  trees 
and  shrubs  ? 

Bark  is  composed  of  matter  which  is.  very  slowly  per- 
meable by  heat,  and,  like  hair  and  fur  in  animals,  is  es- 
pecially adapted  for  securing  the  temperature  necessary 
tg  vegetable  life. 

9SO  What  is  the  temperature  of  the  sap  of  healthy  trees  during  the 
summer  f 

It  is  several  degrees  below  that  of  the  surrounding  at- 
mosphere. 

981    What  is  the  temperature  of  the  sap  of  a  healthy  tree  in  tfie  winter  f 


152  SCIENCE   OF   COMMON   THINGS. 


Temperature  of  trees.  Flannels  and  furs  not  really  warm. 

Several  degrees  above  that  of  the  surrounding  atmo- 
sphere. 

983  What  occasions  this  difference  between  the  temperature  of  the  sap 
of  a  tree  and  the  temperature  of  the  surrounding  atmosphere  1 

The  vital  action  of  the  tree. 

It  is  also  a  noticeable  fact  that  sap  drawn  from  a  tree  will  freeze  at  the 
same  temperature  as  water,  while  the  sap  circulating  in  the  tree,  nnder 
.the  influence  of  vital  agency,  will  not  freeze  until  reduced  seventeen  degrees 
below  the  freezing-point  of  water. 

983  Why  in  a  frozen  pond  or  lake  is  the  ice  always  thinner^  and  often 
entirely  wanting,  in  those  parts  where  springs  exist  upon  the  bottom  1 

Because  the  spring  water,  coining  from  a  point  in 
the  earth  below  the  influence  of  the  frosts,  is  elevated 
in  temperature,  and  by  imparting  its  heat  prevents  an 
accumulation  of  ice  upon  the  surface  above. 

984  Is  there  in  reality  any  positive  warmth  in  the  materials  of  cloth- 
ing? 

No ;  but  we  consider  clothing  warm  or  cool  accord- 
ing as  it  impedes  or  facilitates  the  passage  of  heat  to  or 
from  the  surface  of  our  bodies.  The  thick  cloak  which 
guards  a  Spaniard  against  the  cold  of  winter  is  also  in 
summer  used  by  him  as  a  protection  against  the  direct 
rays  of  the  sun;  and,  while  in  temperate  climates  flan- 
nel is  the  warmest  article  of  dress,  we  cannot  at  the 
same  time  preserve  ice  more  effectually  than  by  inclos- 
ing it  in  its  softest  folds. 

985  Does  fine  or  coarse  woollen  cloth  make  the  warmest  clothing? 

TliQfaier  the  cloth,  the  more  slowly  it  conducts  heat. 
Fine  cloths,  therefore,  are  warmer  than  coarse  ones. 

98S  Is  silk  a  good  conductor  of  heat  f 

~No ;  it  is  a  bad  conductor  of  heat.  Spun  silk  allows 
the  heat  of  the  body  to  pass  off  more  quickly  than  wool ; 
but  raw  silk  confines  it  more  than  wool. 

987*  Tlie  sheets  of  a  bed  feel  cold  and  the  blankets  warm. :  is  there  any 
difference  in  the  respective  temperature  of  these  articles  f 

No ;  the  temperature  of  both  the  sheets  and  the  blan- 
kets is  always  exactly  the  same. 

988    Why,  then,  does  one  feel  colder  than  the  other  f 

Sheets  feel  colder  than  the  blankets  because  they  are 


SCIENCE  OF   COMMON   THINGS.  153 

Coolness  and  warmth  of  the  air.  Conduction  of  heat. 

better  conductors  of  heat,  and  carry  off  the  heat  more 
rapidly  from  the  body ;  but  when  bjr  the  continuance 
of  the  body  between  them  they  acquire  the  same  tem- 
perature, they  will  then  feel  even  warmer  than  the 
blankets. 

989  In  the  summer  a  still,  calm  atmosphere  feels  warm,  but  if  a  wind 
arises,  the  same  atmosphere  feels  cold :  has  there  been  any  real  change  of  tem- 
perature f 

~No  ;  for  a  thermometer  suspended  under  shelter  and 
in  a  calm  place  wrill  indicate  the  same  temperature  as  a 
thermometer  on  which  the  wind  blows. 

990  Why  do  we  then  consider  that  the  air  has  grown  colder  ? 

Because  the  air  in  motion  by  the  wind  conducts  off 
the  heat  from  our  bodies  faster  than  the  same  air  at 
rest. 

991  What  is  meant  by  the  convection  of  heat? 

Heat  communicated  by  being  carried  to  another 
thing  or  place  ;  as  the  hot  water  resting  on  the  bottom 
of  a  kettle  carries  heat  to  the  water  through  which  it 
ascends. 

993  Are  liquids  good  conductors  of  heat  f 

"No ;  liquids  are  bad  conductors;  and  are  therefore 
made  hot  by  convection. 

993  Why  are  liquids  bad  conductors  of  heat  ? 

This  peculiarity  is  referable  to  the  mobility  wrhich 
subsists  among  the  particles  of  all  fluids,  and  to  the 
change  in  the  size  of  the  particles,  which  is  invariably 
produced  by  their  change  in  temperature. 

The  constituent  particles  of  solid  bodies  being  incapable  of  changing 
their  material  position  and  arrangement,  the  heat  can  only  pass  through 
them,  from  particle  to  particle,  by  a  slow  process ;  but  when  the  particles 
forming  any  stratum  of  liquid  are  heated,  their  mass,  expanding,  becomes 
lighter,  bulk  for  bulk,  than  the  colder  stratum  immediately  above  it,  and 
ascends,  allowing  the  superior  strata  to  descend. 

994  Explain  hotu  water  is  made  hot. 

"When  the  heat  enters  at  the  bottom  of  a  vessel  con- 
taining water,  a  double  set  of  currents  is  immediately 
established, — one  of  hot  particles  rising  towards  the 


154 


SCIENCE   OF  COMMON   THINGS. 


How  liquids  are  made  hot. 


Why  water  is  agitated  when  boiling. 


Fig.  38. 


surface,  and  the  other  of  colder  particles 
descending  to  the  bottom.  The  portion  of 
liquid  which  receives  heat  from  below  is 
thus  continually  mixed  through  the  other 
parts,  and  the  heat  is  diffused  by  the  mo- 
tion of  the  particles  among  each  other. 

These  currents  take  place  so  rapidly,  that  if  a  thermo- 
meter be  placed  at  the  bottom  and  another  at  the  top 
of  a  long  jar,  the  fire  being  applied  below,  the  upper  one 
will  begin  to  rise  almost  as  soon  as  the  lower  one.  The 
movement  of  the  particles  of  water  in  boiling  will  be 
understood  by  reference  to  Fig,  38. 

995  What  common  experiment  proves  that  water  is  a  bad  conductor  of 
heat  f 

When  a  blacksmith  immerses  his  red-hot  iron  in  a 
tank  of  water,  the  water  which  surrounds  the  iron  is 
made  boiling  hot,  while  the  water  not  immediately  in 
contact  with  it  remains  quite  cold. 

If  a  tube  nearly  filled  with  water  is 
held  over  a  spirit  lamp,  as  in  Fig.  39,  in 
such  a  manner  as  to  direct  the  flame 
against  the  upper  layers  of  the  water, 
the  water  will  be  observed  to  boil  at  the 
top,  but  remain  cool  below.  If  quicksil- 
ver, on  the  contrary,  be  so  treated,  its 
lower  layers  will  speedily  become  heated. 
The  particles  of  mercury  will  communi- 
cate the  heat  to  each  other,  but  the  particles  of  water  will  not  do  so. 

996  "Why  is  water  in  such  continual  ferment  when  it  is  boiling  ? 

This  commotion  is  mainly  produced  by  the  ascend- 
ing and  descending  currents  of  hot  and  cold  water. 

The  escape  of  steam  from  the  water  contributes  also  to  increase  this 
agitation. 

997*  How  do  these  two  currents  pass  each  oilier  f 

The  hot  ascending  current  rises  up  through  the  centre 
of  the  mass  of  water ;  while  the  cold  descending  cur- 
rents pass  down  by  the  metal  sides  of  the  kettle. 

998    Why  is  heat  applied  to  the  bottom,  and  not  to  the  top  of  the  kettle  ? 

Because  the  heated  water  always  ascends  to  the  sur- 
face^ heating  the  water  through  which  it  passes ;  if, 
therefore,  heat  were  applied  to  the  top  of  a  vessel,  the 
water  below  the  surface  would  be  heated  very  slowly. 


Fig.  39. 


SCIENCE   OF   COMMON   THINGS.  155 

How  to  cool  liquids.  Boiling  point  of  liquids. 

999  As  the  lower  part  of  a  grate  is  made  red  hot  by  the  fire  above,  why 
would  not  the  water  boil  if  fire  were  applied  to  the  top  of  a  kettle  ? 

The  iron  of  a  grate  is  an  excellent  conductor ;  if, 
therefore,  one  part  be  heated,  the  heat  is  conducted  to 
every  other  part ;  but  water  is  a  very  bad  conductor, 
and  will  not  diffuse  heat  in  a  similar  way. 

1000  If  you  wish  to  cool  liquids,  where  should  the  cold  be  applied  f 

To  the  top  of  th«  liquid  /  because  the  cold  portions 
will  always  descend,  and  allow  the  warmer  part  to  come 
in  contact  with  the  cooling  substance. 

1001  Does  boiling  water  get  hotter  by  being  kept  on  the  fire  ? 

No  ;  not  if  the  steam  be  suffered  to  escape. 

1OOS  Why  does  not  boiling  water  get  hotter  if  the  steam  be  suffered  to 
escape  f 

Because  the  water  is  converted  into  steam  as  fast  as 
it  boils ;  and  the  stearn  carries  away  the  additional 
heat, 

1003  What  is  ebullition  f 

"When  a  liquid  substance  is  heated  sufficiently  to 
form  steam,  the  production  of  vapor  takes  place  princi- 
pally at  that  part  where  the  heat  enters ;  and  when  the 
heating  takes  place  not  from  above,  but  from  the  bot- 
tom and  sides,  the  steam  as  it  is  produced  rises  in  bub- 
bles through  the  liquid,  and  produces  the  phenomenon 
of  boiling  or  ebullition. 

1004  What  do  we  mean  by  the  boiling  point  of  a  liquid  ? 

The  temperature  at  which  vapor  rises  with  sufficient 
freedom  to  cause  the  phenomenon  of  ebullition  is  called 
the  boiling  point. 

1005  Do  att  liquids  boil  at  the  same  temperature  f 

No ;  the  boiling  point  occurs  in  different  liquids  at 
very  different  temperatures. 

1006  Why  does  milk  'boil  over  more  readily  than  water  f 

Because  the  bubbles  of  milk,  produced  by  the  pro- 
cess of  boiling,  are  more  tenacious  than  the  bubbles  of 
water ;  and  these  bubbles,  accumulating  and  climbing 
one  above  another,  seon  overtop  the  rim  of  the  saucepan 
and  run  over. 

1007  Why  does  water  simmer  before  it  boils? 


356  SCIENCE   OF   COMMON   THINGS. 

Simmering.  "Why  a  kettle  sometimes  boils  over. 

Because  the  particles  of  water  near  the  bottom  of  the 
kettle  (being  formed  into  steam  sooner  than  the  rest) 
shoot  upwards,  but  are  condensed  again  (as  they  rise) 
~by  the  colder  water,  and  produce  what  is  called  "  sim-. 
mering." 

1008  What  is  meant  by  simmering  } 

A  gentle  tremor  or  undulation  on  the  surface  of  the 
water.  When  water  simmers,  tha  bubbles  collapse 
beneath  the  surface,  and  the  steam  is  condensed  to  water 
again;  but  when  water  boils,  the  bubbles  rise  to  the 
surface,  and  the  steam  is  thrown  off. 

1009  Why  does  boiling  water  swell? 

Because  it  is  expanded  by  the  heat /  that  is,  the  heat 
of  the  fire  drives  the  particles  of  water  farther  apart 
from  each  other,  and  (as  they  are  not  packed  so  closely 
together)  they  take  up  more  room  /  in  other  words,  the 
water  swells. 

1010  Why  does  boiling  water  bubble  ? 

Because  the  vapor  (rising  through  the  water)  is 
diffused,  and  forces  up  bubbles  in  its  effort  to  escape. 

All  the  air  of  water  is  expelled  at  the  commencement  of  its  boiling. 

1011  Why  does  a  kettle  sometimes  boil  over  f 

Because  the  water  is  expanded  by  heat  /  if,  therefore, 
a  kettle  is  filled  with  cold  water,  some  of  it  must  run 
over  as  soon  as  it  is  expanded  by  heat. 

1O1J3  But  I  have  seen  a  kettle  boil  over,  although  it  has  not  been  fitted 
full  of  water :  how  do  you  account  for  that? 

If  a  fire  be  very  fierce,  the  air  and  vapor  are  expelled 
so  rapidly,  that  the  bubbles  are  very  numerous,  and 
(towering  one  above  another)  reach  the  top  of  the  kettle, 
and  fall  over. 

1013  Why  is  a  pot  (which  was  full  to  over/lowing  while  the  water  was 
boiling  hot)  not  full  after  it  has  been  taken  off  the  fire  for  a  short  time  f 

Because  (while  the  water  is  boiling)  it  is  expanded 
by  the  heat,  and  fills  the  pot  even  to  overflowing ;  but 
when  it  becomes  cool,  it  contracts  again,  and  occupies  a 
much  less  space. 

1014  When  steam  pours  out  from  the  ''spout  of  a  kettle,  the  stream 
"begins  apparently  half  an  inch  off  Hie  spout :  why  does  it  not  begin  close  to 
the  spout  f 


SCIENCE   OF   COMMON   THINGS.  157 

Steam  is  invisible.  Liquids  become  no  hotter  after  boiling. 

Steam  is  really  invisible  /  and  the  half  inch  (between 
the  spout  and  the  "  stream  of  mist")  is  the  real  steam, 
before  it  has  been  condensed  by  air. 

1O15   Why  is  not  all  the  steam  invisible  as  well  as  that  half  inch  ? 

Because  the  invisible  particles  are  condensed  ly  the 
cold  air,  and,  rolling  one  into  another,  look  like  a  thick 
mist. 

1O1B    What  becomes  of  the  steam,  for  it  soon  vanisJies  f 

After  it  has  been  condensed  into  mist,  it  is  dissolved 
by  the  air,  and  dispersed  abroad  as  invisible  vapor. 

lOlT*  And  what  becomes  of  the  invisible  vapor  f 

Being  lighter  than  air,  it  ascends  to  the  upper  regions 
of  the  atmosphere,  where  (being  again  condensed)  it  con- 
tributes to  form  clouds. 

1O1S   Why  do  sugar,  salt,  &c.,  retard  the  progress  of  boiling  f 

Because  they  increase  the  density  of  water ;  and 
whatever  increases  the  density  of  a  fluid  retards  its 
boiling. 

1O19    Why  can  liquids  impart  no  additional  heat  after  they  boil  f 

Because  all  additional  heat  is  spent  in  making  steam. 
Hence  wrater  will  not  boil  a  vessel  of  water  immersed  in 
it,  because  it  cannot  impart  to  it  212°  of  heat;  but 
"brine  wTill,  because  it  can  impart  more  than  212°  of  heat 
before  it  is  itself  converted  into  steam. 


Ether  .     .  boils  at  100  degrees 
Alcohol   .  .     "       173|     " 
Water .    .  .    l(        212       " 
Water,  with  one- fifth  salt, 
boils  at.  .         .  219       " 


Syrup  .  .  boils  at  221  degrees. 
Oil  of  turpentine     314       " 
Sulphuric  acid         472       " 
Linseed  oil       "      640       " 
Mercury  .  .      "      656       " 


Any  liquid  which  boils  at  a  lower  degree,  can  be  made  to  boil  if  im- 
mersed in  a  liquid  which  boils  at  a  higher  degree.  Thus  a  cup  of  ether 
can  be  made  to  boil  in  a  vessel  of  water ;  a  cup  of  water,  in  a  vessel  of 
brine  or  syrup ;  but  a  cup  of  water  will  not  boil  if  immersed  in  ether,  nor 
a  cup  of  syrup  in  water. 

1OJ3O  Is  the  boiling  point  of  the  same  liquid  always  constant  ? 

Yes,  under  the  same  conditions  /  but  it  is  liable  to  be 
affected  by  various  circumstances. 

1OS1  What  cause  has  a  powerful  influence  in  regulating  the  boiling 
point  of  liquids  f 

The  pressure  of  the  atmosphere  :  if  the  pressure  be 


158  SCIENCE   OF   COMMON  THINGS. 


Influence  of  atmospheric  pressure  on  the  boiling  point.        How  air  is  heated. 

less  than  usual,  then  the  boiling  point  of  water  and  all 
other  liquids  will  be  lower  than  usual ;  if  the  pressure 
increases,  and  the  barometer  rises,  the  temperature  of 
ebullition  will  be  proportionably  increased. 

1OSS  If  the  atmospheric  pressure  be  entirely  removed,  or  if  water  be 
made  to  boil  in  a  vacuum,  at  what  temperature  will  ebullition  commence  ? 

At  a  point  140°  lower  than  in  the  open  air. 

1053  To  what  temperature  can  water  exposed  to  the  air  be  heated  under 
ordinary  circumstances  ? 

To  about  212°  Fahrenheit ;  at  this  temperature  water 
passes  into  steam  or  vapor. 

1054  Can  water  be  heated  beyond  212°  ? 

Yes ;  if  subjected  to  sufficient  pressure,  it  can  be  heated 
to  any  extent  without  boiling.  There  is  no  limit  to  the 
degree  to  which  water  may  be  heated,  provided  the 
vessel  is  strong  enough  to  confine  the  vapor ;  but  the 
expansive  force  of  steam  is  so  enormous  under  these 
circumstances,  as  to  overcome  the  greatest  resistance  , 
which  has  ever  been  exerted  upon  it. 

1055  Why  does  soup  keep  hot  longer  than  boiling  water  f  { 

Because  the  grease  and  other  ingredients  floating  irf 
the  soup  retain  the  heat  longer  than  the  particles  of 
water,  and,  at  the  same  time,  by  their  viscidity  or  tena- 
city, prevent  the  circulation  of  the  heated  particles. 

lOSe  How  is  air  heated? 

By  " connective  currents" 

lOST*  Explain  what  is  meant  by  "  convective  currents" 

When  a  portion  of  air  is  heated,  it  rises  upwards  in 
a  current,  carrying  the  heat  with  it ;  other  colder  air 
succeeds,  and  (being  heated  in  a  similar  wTay)  ascends 
also  :  these  are  called  "  convective  currents." 

"  Convective  currents"  so  called  from  the  Latin  words  cumvectus  (carried 
with),  because  the  heat  is  "carried  with"  the  current. 

1058  Is  air  heated  by  the  rays  of  the  sun  f 

"N6 ;  air  is  not  heated  (to  any  very  great  extent)  Inj  the 
action  of  the  surfs  rays  passing  through  it. 

1059  Why,  then,  is  the  air  hotter  on  a  sunny  day  than  on  a  cloudy 
one? 


SCIENCE   OF   COMMON   THINGS.  159 

How  hot  substances  are  cooled.  Blowing  hot  food  cools  it 

Because  the  sun  heats  the  surface  of  the  earth,  and 
the  air  (resting  on  the  earth)  is  heated  by  contact  /  as 
soon  as  it  is  heated  it  ascends,  while  its  place  is  sup- 
plied by  colder  portions,  which  are  heated  in  turn  also. 

1030  If  air  be  a  bad  conductor,  why  does  hot  iron  become  cold  by  expo- 
sure to  the  airf 

Because  it  is  made  cold — 1.  By  "  convection ;"  and 
2.  By  "  radiation." 

1031  How  is  hot  iron  made,  cold  by  convection  ? 

The  air  resting  on  the  hot  iron  (being  intensely  heated) 
rapidly  ascends  with  the  heat  it  has  absorbed ;  colder 
air  succeeding,  absorbs  more  heat  and  ascends  also ;  and 
this  process  is  repeated  till  the  hot  iron  is  cooled  com- 
pletely down. 

ICpSS  How  is  broth  cooled  by  being  left  exposed  to  the  air  f 

It  throws  o&some  heat  by  radiation  •  but  it  is  mainly 
cooled  down  by  convection. 

1033  How  is  hot  broth  cooled  down  by  convection  1 

The  air  resting  on  the  hot  broth  (being  heated)  as- 
cends ,\\  colder  air  succeeding  absorbs  more  heat,  and 
ascends  also  ;  and  this  process  is  repeated  till  the  broth 
is  made  cool. 

1  The  particles  on  the  surface  of  the  broth  sink  as  they  are  cooled  down, 
and  warmer  particles  rise  to  the  surface,  which  gradually  assist  the  cool- 
ing process. 

1034  Why  are  hot  tea  and  broth  cooled  faster  by  being  stirred  about  f 

1.  Because  the  agitation  assists  in  bringing  its  hottest 
particles  to  the  surface  • 

2.  As  the  hotter  particles  are  more  rapidly  brought 
into  contact  with  the  air,  therefore  cqnvection  is  more 
rapid. 

1035  How  does  bloiving  hot  food  make  it  coolf 

It  causes  the  air  (which  has  been  heated  by  the 
food)  to  change  more  rapidly F,  and  give  place  to  fresh 
cold  air. 

1036  If  a  shutter  be  closed  in  the  daytime,  the  stream  of  light  (pierc- 
ing through  the  crevice)  seems  in  constant  agitation :  why  is  this  f 

Because  little  motes  and  particles  of  dust  (thrown  into 


160  SCIENCE    OF   COMMON   THINGS. 


Milk  boila  qv.lcker  than  water.     Why  stoves  are  not  placed  at  top  of  the  room. 

agitation  by  the  violence  of  the  convective  currents)  are 
made  visible  by  the  strong  beam  of  light  thrown  into 
the  room  through  the  crevice  of  the  shutter. 

1O37*    Why  does  milk  boil  more  quickly  than  tvater? 

Milk  is  a  thicker  liquid  than  water,  and  consequently 
less  steam  escapes  through  the  thick  liquid  (milk)  than 
through  the  thin  liquid  (water)  ;  therefore  the  heat  of 
the  whole  mass  of  the  milk  rises  more  quickly. 

1O3Q  Why  are  fires  placed  near  the  floor  of  a  room,  and  not  towards 
the  ceiling  ? 

Because  heated  air  always  ascends.  If,  therefore, 
the  fire  were  not  near  the  floor,  the  air  of  the  lower 
part  of  the  room  would  be  elevated  in  temperature  very 
slowly. 

1039  Would  not  the  air  of  the  lower  part  of  a  room  be  heated  equally 
well  if  the  fires  were  fixed  higher  up  f 

No ;  the  heat  of  a  fire  has  a  very  little  effect  upon 
the  air  'below  the  level  of  the  fire  /  and  therefore  every 
fire  should  be  as  near  to  the  floor  possible. 

1040  Our  feet  are  very  frequently  cold  when  we  sit  close  by  a  good  fire  : 
explain  the  reason  of  this  ? 

As  the  air  over  the  fire  becomes  heated  and  rises, 
cold  air  rushes  through  the  crevices  of  the  doors  and 
windows,  and  along  the  bottom  of  the  room,  to  supply 
the  deficiency  ;  and  these  currents  of  cold  air  rushing 
constantly  over  our  feet,  deprive  them  of  their  warmth. 

104:1    What  is  meant  by  radiation  of  heat  f 

The  emission  of  rays  of  heat  in  all  directions. 

"When  the  hand  is  placed  near  a  hot  body  suspended  in  the  air,  a  sen- 
sation of  warmth  is  perceived,  even  for  a  considerable  distance.  If  the 
hand  be  held  beneath  the  body,  the  sensation  will  be  as  great  as  upon 
the  sides,  although  the  heat  has  to  shoot  down  through  an  opposing  cur- 
rent of  air  approaching  it.  This  effect  does  not  arise  from  the  heat  being 
conveyed  by  means  of  a  hot  current,  since  all  the  heated  particles  have  a 
uniform  tendencj^  to  rise;  neither  can  it  depend  upon  the  conducting 
power  of  the  air,  because  aerial  substances  possess  that  power  in  a  very 
low  degree,  while  the  sensation  in  the  present  case  is  excited  almost  on 
the  instant.  This  method  of  distributing  heat,  to  distinguish  it  from  heat 
passing  by  contact  or  conduction,  is  called  radiation. 

1O4S  How  do  we  designate  heat  so  distributed  f 

As  radiant  or  radiated  heat. 


SCIENCE   OF   COMMON   THINGS.  161 


Radiation.  Good  and  bad  radiators. 


1043  When  is  heat  radiated  from  one  body  to  another  ? 

When  the  two  bodies  are  separated  by  a  non-con- 
ducting medium. 

1044  On  ivliat  does  radiation  depend  f 

On  the  roughness  of  the  radiating  surface  :  thus,  if 
metal  be  scratched,  its  radiating  power  is  increased, 
because  the  heat  has  more  points  to  escape  from. 

1045  Does  a  fire  radiate  heat  f 

Yes  ;  and  because  burning  fuel  emits  rays  of  heat, 
we  feel  warm  when  we  stand  before  a  fire. 

1046  Why  does  our  face  feel  uncomfortably  hot  when  we  approach  a 
fire? 

Because  the  fire  radiates  heat  upon  the  face,  which 
(not  being  covered)  feels  the  effect  immediately. 

1047*  Why  does  the  fire  heat  the  face  more  than  it  does  the  rest  of  the 
body  ? 

Because  the  rest  of  the  body  is  covered  with  cloth- 
ing ;  which  (being  a  bad  conductor  of  heat)  prevents 
the  same  sudden  and  rapid  transmission  of  heat  to  the 
skin. 

1O48  Do  those  substances  which  radiate  heat  absorb  heat  also  f 

Yes.  Those  substances  which  radiate  most  also 
absorb  most  heat ;  and  those  which  radiate  least  also 
absorb  the  least  heat. 

1O4Q  Does  any  thing  else  radiate  heat  besides  the  sun  and  fire  f 

Yes ;  all  things  radiate  heat  in  some  measure,  but 
not  equally  well. 

1050  What  things  radiate  heat  the  next  best  to  the  sun  and  fire  f 

All  dull  and  dark  substances  are  good  radiators  of 
heat ;  but  all  light  and  polished  substa'nces  are  lad  ra- 
diators. 

1051  What  is  meant  by  being  a  "  bad  radiator  of  heat  ?" 

To  radiate  heat  is  to  throw  off  heat  ~by  rays,  as  the 
sun  ;  a  polished  tin  pan  does  not  throw  off  the  heat  of 
boiling  water  from  its  surface,  but  keeps  it  in. 

1O553  Why  does  snow  (at  the  foot  of  a  tree  or  wall)  melt  sooner  than  in 
an  open  field  ? 


162  SCIENCE   OF   COMMON   THINGS. 

Utility  of  blackening  stoves.  Bright  metal  retains  heat.  Dew. 

Because  the  tree  or  wall  radiates  heat  into  the  snow 
beneath,  which  melts  it. 

1053  Why  sliould  the  flues  (connected  with  stoves,  etc.)  be  always  black- 
ened with  black  lead  f 

In  order  that  the  heat  of  the  flue  may  be  more  readi- 
ly diffused  throughout  the  room.  Black  lead  radiates 
heat  more  freely  than  any  other  known  substance. 

1054  Would  a  metal  pot  serve  to  keep  water  hot  if  it  were  dull  and 
dirty  f 

'No ;  it  is  the  bright  polish  of  the  metal  which  makes 
it  a  bad  radiator ;  it  it  were  dull,  scratched,  or  dirty, 
the  heat  would  escape  very  rapidly. 

"Water  in  hot  weather  is  also  kept  cookr  in  bright  metal  than  in  dull  or 
earthen  vessels. 

1055  Why  are  dinner-covers  made  of  bright  tin  or  silver? 

Because  li^ht-colored  and  highly-polished  metal  is  a 
very  bad  radiator  of  heat  /  and  therefore  bright  tin  or 
silver  will  not  allow  the  heat  of  the  cooked  food  to  es- 
cape through  the  cover  by  radiation. 


CHAPTER   Y. 

THE   PHENOMENA   OF   DEW. 
1O5B   What  is  Dew  f 

Dew  is  the  moisture  of  the  air  condensed  by  coming 
in  contact  with  bodies  colder  than  itself. 

1O57*   Why  is  the  ground  sometimes  covered  with  dew  ? 

Because  the  surface  of  the  earth  (at  sunset)  is  made 
so  very  cold  by  radiation,  that  the  warm  vapor  of  the 
air  is  chilled  by  contact,  and  condensed  into  dew. 

1O58   Why  is  the  earth  made  colder  than  the  air  after  the  sun  has  set  f 

Because  the  earth  radiates  heat  very  freely,  but  the 


SCIENCE   OF  COMMON  THINGS.  163 

Cause  of  dew.    When  most  dew  is  deposited.    Difference  between  dew  and  rain. 


air  does  not ;  in  consequence  of  which  the  earth  is 
often  five  or  ten  degrees  colder  than  the  air  (after  sun- 
set), although  it  may  have  been  warmer  than  the  air 
during  the  whole  day. 

1O5Q  Why  is  the  surface  of  the  earth  generally  warmer  than  the  air 
during  the  day  t 

Because  the  earth  absorbs  solar  heat  very  freely,  but 
the  air  does  not;  in  consequence  of  which  it  is  often 
many  degrees  warmer  than  the  air  during  the  day. 

1O6O  Why  is  the  surface  of  the  ground  colder  in  a  fine  night  than  in  a 
cloudy  one  ? 

Because  on  a  fine,  clear,  starlight  night,  heat  radiates 
from  the  earth  freely,  and  is  lost  in  open  space ;  but 
on  a  dull  night,  the  clouds  arrest  the  process  of  radi- 
ation. 

1OQ1   Why  is  dew  deposited  inost  readily  on  a  fine,  clear  night  f 

Because  the  surface  of  the  ground  radiates  heat  most 
freely^  on  a  fine  night,  and  (being  cooled  down  by  this 
loss  of  heat)  chills  the  vapor  of  the  air  into  dew. 

1O©S    Why  is  there  no  dew  on  a  dull,  cloudy  night? 

Because  the  clouds  arrest  the  radiation  of  heat  from, 
the  earth,  and  (as  the  heat  cannot  freely  escape)  the 
surface  is  not  sufficiently  cooled  down  to  chill  the  vapor 
of  the  air  into  dew. 

1OQ3   Why  is  a  cloudy  night  warmer  than  a  fine,  clear  night? 

Because  the  clouds  prevent  the  radiation  of  heat  from 
the  earth  ;  in  consequence  of  which  the  surface  of  the 
earth  remains  warmer. 

1OQ-1  How  do  clouds  arrest  or  prevent  the  radiation  of  heat  from  the 
earth? 

The  lower  surfaces  of  the  clouds  turn  hack  the  rays 
of  heat  as  they  radiate  or  pass  off  from  the  earth,  and 
prevent  their  dispersion  into  space. 

1065  What  is  the  difference  between  dew  and  rain? 

In  dew,  the  condensation  is  made  near  the  earth's 
surface.  In  rain,  the  drops  fall  from  a  considerable 
height. 

1066  What  is  the  cause  of  loth  dew  and  rain  f 


SCIENCE   OF   COMMON   THINGS. 


Situations  in  which  no  dew  is  deposited. 


Cold  condensing  the  vapor  of  the  air  wlien  near  the 
point  of  saturation. 

1067*   Why  do  mist  and  fog  vanish  at  sunrise1} 

Because  the  condensed  particles  are  again  changed 
into  invisible  vapor  by  the  heat  of  the  sun. 

1068  Why  is  dew  most  abundant  in  situations  most  exposed? 

Because  the  radiation  of  heat  is  not  arrested  by 
houses,  trees,  hedges,  or  any  other  thing. 

1069  Why  is  there  scarcely  any  dew  under  a  leafy  tree  ? 

1.  Because  the  thick  foliage  of  a  tree  arrests  the  radi- 
ation of  heat  from  the  earth  ;  and 

2.  A  leafy  tree  radiates  some  of  its  own  heat  towards 
the  earth  •  in  consequence  of  which  the  ground  under- 
neath a  tree  is  not  sufficiently  cooled  down  to  chill  the 
vapor  of  the  air  into  dew. 

1070  Why  is  there  never  much  dew  at  the  foot  of  walls  and  hedges? 

1.  Because  they  act  as  screens  to  arrest  the  radiation 
of  heat  from  the  earth  ;  and 

2.  They  themselves  radiate  some  portion   of  heat 
towards  the  earth  ;  in  consequence  of  which  the  ground 
at  the  foot  of  walls  and  hedges  is  not  sufficiently  cooled 
down  to  chill  the  vapor  of  the  air  into  dew. 

1O7*1    Why  is  there  no  dew  on  a  windy  night  % 

1.  Because  the  wind  evaporates  the  moisture  as  fast 
as  it  is  deposited  ;  and 

2.  It  disturbs  the  radiation  of  heat,  and  thus  dimi- 
nishes the  deposition  of  dew. 

1O7*!3  Why  are  valleys  and  hollows  often  thickly  covered  with  dew, 
although  they  are  sheltered  f 

Because  the  surrounding  hills  prevent  the  agitation 
of  the  air,  but  do  not  overhang  and  screen  the  valleys 
sufficiently  to  arrest  the  radiation  from  their  surfaces. 

1O7*3  Why  does  dew  fatt  more  abundantly  on  some  substances  than  on 
others? 

Because  some  substances  radiate  heat  more  freely 
than  others,  and  therefore  become  much  cooler  in  the 
night. 


SCIENCE   OF   COMMON    THINGS.  165 

Plants  requiring  the  most  moisture  condense  the  most  dew. 

107*4:  Why  are  substances  which  radiate  the  heat  most  freely  always 
the  most  thickly  covered  with  dew  ? 

Because  they  are  the  coldest  substances,  and  there- 
fore condense  vapor  most  readily. 

107*5    What  kind  of  materials  radiate  heat  most  freely  f 

Grass,  wood,  and  the  leaves  of  plants  radiate  heat 
very  freely  •  but  polished  metal,  smooth  stones,  and 
woollen  cloth  part  with  their  heat  very  tardily. 

1O7*6  Do  the  kaves  of  all  plants  radiate  heat  equally  well? 

No.  Rough,  woolly  leaves  (like  those  of  a  hollyhock) 
radiate  heat  much  more  freely  than  hard,  smooth  po- 
lished leaves,  like  those  of  the  common  laurel. 

1O7*7*  Show  the  wisdom  of  the  Creator  in  making  grass,  the  kaves  of 
trees,  and  all  vegetables,  excellent  radiators  of  heat  ? 

As  vegetables  require  much  moisture,  and  would 
often  perish  without  a  plentiful  deposit  of  dew,  the 
Creator  wisely  made  them  to  radiate  heat  freely,  so  as 
to  chill  the  vapor  (which  touches  them)  into  dew. 

1O7*S  Will  polished  metal,  smooth  stones,  and  woollen  doth  readily  col- 
lect dew  f 

No.  "While  grass  and  leaves  of  plants  are  completely 
drenched  with  dew,  a  piece  of  polished  metal  or  of 
woollen  cloth  (lying  on  the  same  spot)  will  be  almost 
dry. 

1O7*9  Why  would  polished  metal  and  woollen  cloth  le  dry,  while  grass 
and  leaves  are  drencJied  with  deiv  % 

Because  the  polished  metal  and  woollen  cloth  part 
with  their  heat  so  slowly,  that  the  vapor  of  the  air  is 
not  chilled  into  dew  as  it  passes  over  them, 

1OSO  Why  is  a  gravel  walk  almost  dry  wlien  a  grass-plat  is  covered 
fliick  with  dew  ? 

Because  grass  is  a  good  radiator,  and  throws  off  its 
heat  very  freely  ;  but  gravel  is  a  very  l>ad  radiator, 
and  parts  writh  its  heat  very  slowly.  • 

1O81  Is  that  the  reason  why  grass  is  saturated  with  dew,  and  the  gra- 
vel is  not  f 

Yes.  When  the  vapor  of  warm  air  comes  in  contact 
with  the  cold  grass,  it  is  instantly  chilled  into  dew ;  but 


168  SCIENCE   OF  COMMON   THINGS. 


Dew  on  rocky  and  on  fertile  Boils.  Dew  most  abundant  after  a  hot  day. 

it  is  not  so  freely  condensed  as  it  passes  over  gravel, 
because  gravel  is  not  so  cold  as  the  grass. 

1O8S    Why  does  dew  rarely  fall  upon  hard  rocks  and  barren  lands  ? 

Because  rocks  and  barren  lands  are  so  compact  and 
hard,  that  they  can  neither  absorb,  nor  radiate  much 
heat  /  and  (as  their  temperature  varies  but  very -little) 
very  little  dew  deposits  upon  them. 

1O83  Why  does  dew  fall  more  abundantly  on  cultivated  soils  than  on 
barren  lands  f 

Because  cultivated  soils  (being  loose  and  porous) 
very  freely  radiate  by  night  the  heat  which  they  ab- 
sorb by  day ;  in  consequence  of  which  they  are  much 
cooled  down,  and  plentifully  condense  the  vapor  of  the 
passing  air  into  dew. 

1OS4  Show  the  wisdom  of  the  Creator  in  this  arrangement  f 

Every  plant  and  inch  of  land  which  needs  the  moist- 
ure of  dew  is  adapted  to  collect  it ;  but  not  a  single 
drop  is  wasted  where  its  refreshing  moisture  is  not 
required. 

1O85    When  is  dew  most  copiously  distilled  t 

After  a  hot  day  in  summer  or  autumn,  especially  if 
the  wind  blows  over  a  body  of  water. 

1OSG    Why  is  dew  distilled  most  copiously  after  a  hot  day  ? 

Because  the  surface  of  the  hot  earth  radiates  heat 
very  freely  at  sunset,  and  (being  made  much  colder 
than  the  air)  chills  the  passing  vapor  and  condenses  it 
into  dew. 

108*7  Why  is  there  less  dew  when  the  wind  blows  across  the  land,  than 
when  it  blows  over  a  body  of  water  ? 

Because  the  winds  which  blow  across  the.Zan^  are 
dry  and  arid  /  but  those  which  cross  the  water  are 
moist  and  full  of  vapor. 

1088  How  does  the  dryness  of  the  wind  prevent  dew-falls? 

As  winds  (currents  of  air)  which  blow  over  the  land 
are  very  dry,  they  imbibe  the  moisture  of  the  air ;  in 
consequence  of  which  there  is  very  little  left  to  be  con- 
densed into  dew. 

1089  Why  is  meal  very  subject  to  faint  on  a  moonlight  niyhtt 


SCIENCE   OF   COMMON   THINGS.  167 

Protection  against  frost.  Cause  of  fog  and  mist. 

Because  it  radiates  heat  very  freely  in  a  bright  moon- 
light night ;  in  consequence  of  which  it  is  soon  covered 
with  dew,  which  produces  rapid  decomposition. 

1O0  O  How  do  moonlight  nights  conduce  to  the  rapid  growth  of  plants  f 

Radiation  is  carried  on  very  rapidly  on  bright  moon- 
light nights  ;  in  consequence  of  which  dew  is  very 
plentifully  deposited  on  young  plants,  which  conduces 
much  to  their  growth  and  vigor. 

1O91  Why  is  the  air  in  immediate  contact  with  the  earth,  on  a  clear 
night,  cooler  than  tlie  air  at  a  little  distance  from  the  surface  f 

Because  it  parts  with  its  heat  to  the  earth,  which  in 
turn  loses  it  by  radiation. 

1O93  How  can  a  thin  covering  of  bass,  or  even  muslin,  protect  trees 
from  frost  ? 

Because  any  covering  prevents  the  radiation  of  heat 
from  the  tree  ;  and  if  trees  are  not  cooled  down  by  radi- 
ation, the  vapor  of  the  air  will  not  fe frozen  as  it  comes 
in  contact  with  them. 

Bass — a  kind  of  matting  used  by  gardeners. 

1093  Why  is  the  bass  or  canvas  itself  (which  covers  the  tree)  ahvays 
drenched  with  deiv  ? 

Because  it  radiates  heat  both  upwards  and  down- 
wards j  in  consequence  of  which  it  is  so  cooled  down 
that  it  readily  chills  the  vapor  of  the  air  into  dew. 

1094  What  is  the  cause  of  mist  or  earth-fog  ? 

If  the  night  has  been  very  calm,  the  radiation  of  heat 
from  the  earth  has  been  very  abundant ;  in  consequence 
of  which  the  air  (resting  on  the  earth)  has  been  chilled, 
and  its  vapor  condensed  into  a  thick  mist. 

1095  Why  does  not  the  mist  become  devj  ? 

Because  the  chill  of  the  air  is  so  rapid,  that  vapor  is 
condensedy^site/'  than  it  can  be  deposited  and  (covering 
the  earth  as  a  mist)  prevents  any  farther  radiation  of 
heat  from  the  earth. 

1096  When  the  earth  can  no  longer  radiate  heat  upwards,  does  it  con- 
tinue to  condense  the  vapor  of  the  air  ? 

No ;  the  air  (in  contact  with  the  earth)  becomes  about 
equal  in  temperature  with  the  surface  of  the  earth  itself; 


168  SCIENCE   OF   COMMON   THINGS. 

Mist  and  dew  vanish  at  sunrise.  No  dew  in  cities. 

for  which  reason  the  mist  is  not  condensed  into  dew^  but 
remains  floating  above  the  earth  as  a  thick  cloud. 

1097*  This  mitt  seems  to  rise  higher  and  higher,  and  yet  remains  quite 
as  dense  below  as  at  first :  explain  the  cause  of  this. 

The  air  resting  on  the  earth  is  first  chilled,  and  chills 
the  air  resting  on  it ;  the  air  which  touches  this  new 
layer  of  mist  being  also  condensed,  layer  is  added  to 
layer ;  and  thus  the  mist  seems  to  be  rising,  when  (in 
fact)  it  is  only  deepening. 

1O08    Why  do  mist  and  dew  vanish  as  the  sun  rises  f 

Because  the  air  becomes  warmer  at  sunrise,  and  ab- 
sorbs the  vapor. 

1OS9   Can  the  dew  properly  be  said  to  "fall?" 

Kow  ;  dew  is  a\w&ys  formed  upon  the  surface  of  the 
material  upon  which  it  is  found,  and  does  not  fall  from 
the  atmosphere. 

1100  Does  the  color  of  an  object  influence  the  deposition  of  dew  f 

It  does  to  a  considerable  extent. 

1101  How  can  this  be  sliown  f 

If  we  take  pieces  of  red,  black,  green,  and  yellow 
glass,  and  expose  them  when  the  dew  is  condensing,  we 
shall  find  that  moisture  will  show  itself  first  on  the 
yellow  and  then  on  the  green  glass,  but  that  none  will 
appear  on  the  red  or  black  glass.  The  same  thing  will 
take  place  if  we  expose  colored  fluids  in  white  glass 
bottles. 

11O3  Why  is  the  deposition  of  dew  rarely  observed  in  the  close  and 
sheltered  streets  of  cities  f 

•  Because  there  the  objects  are  necessarily  exposed  to 
each  other's  radiation,  and  an  interchange  of  heat  takes 
place,  which  maintains  them  at  a  temperature  uniform 
with  the  air. 

1103  When  is  dew  converted  into  frost  f  \ 

If  the  temperature  of  the  earth,  or  of  the  vessel,  sink 
to  the  freezing  point  or  below,  the  moisture  will  be  de- 
posited as  before ;  but  by  freezing,  it  assumes  the  solid 
Ibrm,  and  is  called  frost. 

1104  Why  is  a  deiv-drop  round  f 


SCIENCE   OF   COMMON   THINGS.  169 

Why  a  dew-drop  is  round.  AVhy  a  duck  is  not  wet  with  water. 

Because  every  part  of  it  is  equally  balanced  ;  and 
therefore  there  is  no  cause  why  one  part  of  the  drop 
should  be  farther  from  the  centre  than  another. 

11O5  Why  will  dew-drops  roll  about  cabbage  plants,  poppies,  &c.,  with- 
out wetting  the  surface  ? 

Because  the  leaves  of  cabbages  and  poppies  are 
covered  with  a  very  fine  waxen  powder,  over  which  the 
dew-drop  rolls  without  wetting  the  surface,  as  a  drop  of 
rain  would  over  dust. 

HO 6  Why  does  not  a  drop  of  rain  wet  the  dust  over  which  it  rottsf 

Because  dust  has  no  affinity  for  w^ater,  and  therefore 
repels  it. 

HOT*  Why  can  swans  and  ducks  dive  under  water  vnthout  being  wetted  1 

Because  their  feathers  are  covered  with  an  oily  secre- 
tion, which  has  no  affinity  for  water,  and  therefore  re- 
pels it. 

11O8  WJiat  is  tlie  figure  which  water  always  assumes  when  unsupported, 
or  supported  on  a  surface  having  little  attraction  for  it? 

The  figure  of  a  sphere.  This  figure  becomes  more  or 
less  globular  or  spheroidal  in  its  shape,  as  the  attraction 
of  the  substances  upon  which  it  is  received  increases  or 
diminishes  ? 

11O0  What  is  the  form  of  a  drop  of  rain  when  descending  in  the  air? 

A  sphere. 

±11O  Why  should  drops  of  water,  resting  upon  surfaces  which  have  no 
affinity  for  them,  assume  a  spheroidal  shape? 

Because  such  surfaces  not  having  so  great  an  attrac- 
tion for  the  drops  of  water  as  the  particles  of  water  have 
for  each  other,  the  drops  tend  to  preserve,  as  nearly  as 
possible,  the  spheroidal  form  which  they  would  have 
if  entirely  unsupported,  as  when  falling  as  drops  of 
rain. 

1111  Is  dew  ever  formed  upon  the  surface  of  water  ? 

The  formation  of  dew  upon  ships  which  traverse  the 
vast  solitudes  of  the  ocean  has  never  been  noticed ;  and 
it  has  been  ascertained  by  experiment  that  even  a  small 
quantity  of  water  gains  no  weight  by  exposure  during 
a  single  night. 


170  SCIENCE   OF   COMMON   THINGS. 


No  dew  on  the  ocean.  No  dew  falls  on  the  human  body. 


Although  dew  dcx  s  not  appear  upon  ships  at  a  great  distance  from  land, 
it  is  freely  deposited  on  the  same  vessels  arriving  in  the  vicinity  of  terra 
firma.  Thus,  navigators  who  proceed  from  the  Straits  of  Sunda  to  the 
Coromandel  coast,  know  that  they  are  near  the  end  of  the  voyage  when 
they  perceive  the  ropes,  sails,  and  other  objects  placed  on  the  deck  become 
moistened  with  dew  during  the  night. 

1112  Why  does  not  dew  form  upon  the  surface  of  water  ? 

Because  whenever  the  aqueous  particles  at  the  sur- 
face are  cooled,  they  become  heavier  than  those  below 
uiein,  and  sink,  while  warmer  arid  lighter  particles  rise 
to  the  top.  These,  in  their  turn,  become  heavier,  and 
descend;  and  the  process,  continuing  throughout  the 
night,  maintains  the  surface  of  the  water  and  the  air  at 
nearly  the  same  temperature. 

1113  Is  the  temperature  at  which  dew  is  deposited  from  the  air  always 
the  same  ? 

No  ;  when  the  air  is  saturated  with  moisture,  a  slight 
reduction  of  temperature  occasions  a  deposition  of  dew; 
but  when  the  air  is  very  dry,  a  greater  reduction  of 
temperature  is  necessary  to  condense  its  vapor. 

1114  Why  are  the  exposed  parts  of  the  human  body  never  covered  with 
deiv? 

Because  the  vital  heat,  varying  from  96°  to  98°  Fah- 
renheit, effectually  prevents  such  a  loss  of  warmth  as  is 
necessary  to  its  production. 

1115  In  what  countries  are  the  dews  most  copious  and  abundant  ? 

In  tropical  climates. 

1116  What  is  the  reason  of  this  f 

Because  in  those  countries  there  is  the  greatest  dif- 
ference between  the  temperature  of  the  day  and  that 
of  the  night. 

The  development  of  vegetation  is  greatest  in  tropical  countries,  and  a 
great  part  of  the  nocturnal  cooling  is  due  to  the  leaves,  which  present  to 
the  sky  ?.T\  immense  number  of  thin  bodies,  having  large  surface,  well 
adapted  to  -radiate  heat. 


SCIENCE    OF   COMMON   THINGS.  171 

Reflection  of  heat.  What  are  rays  of  heat  f 


CHAPTER   YI 

REFLECTION,    ABSORPTION,    AND    TRANSMISSION   OF   HEAT. 

1117  What  is  meant  by  the  reflection  of  heat  f 

Heat  is  said  to  be  reflected  when  it  is  caused  to  re- 
"bound  or  be  thrown  back  from  the  surface  of  a  reflect- 
ing body. 

1118  What  are  the  best  reflectors  of  heat  f 

All  bright  surfaces  and  light  colors. 

1119  Are  good  absorbers  of  heat  good  reflectors  also  ? 

No  ;  those  things  which  absorb  heat  best  reflect  heat 
worst  •  and  those  which  reflect  heat  worst  absorb  it  best. 

1130  Why  are  those  things  which  absorb  heat  unable  to  reflect  it  f 

Because  if  anything  sucks  in  heat,  as  a  sponge  does 
water,  it  cannot  throw  it  off  from  its  surface  ;  and  if 
anything  throws  off  heat  from  its  surface,  it  cannot 
drink  it  in. 

1131  Why  are  reflectors  always  made  of  light-colored  and  highly- 
polished  metal  f 

Because  light-colored  and  highly-polished  metal  makes 
the  best  of  all  reflectors. 


If  metal  be  such  an  excellent  conductor  of  heat,  how  can  it  reflect 
heat,  or  throw  it  off? 

Polished  metal  is  a  conductor  of  heat  only  when  that 
heat  is  communicated  by  actual  contact;  but  when- 
ever heat  falls  upon  bright  metal  in  rays*  it  is  reflected 
back  again,  and  the  metal  remains  cool,. 

1133  What  is  meant  "  by  heat  falling  upon  metal  in  rays"  and  not 
"  by  contact  ?" 

If  a  piece  of  metal  were  thrust  into  a  fire,  it  would 
be  in  actual  contact  with  the  fire  ;  but  if  it  were  held 
before  a  flre^  the  heat  of  the  fire  would  fall  upon  it  in 
rays. 

1134  Why  will  a  kettle  be  slower  in  boiling  if  the  bottom  and  sides  are 
clean  and  bright  f 


172  SCIENCE   OF  COMMON   THINGS. 

Use  of  white  dresses  in  summer.  Coldness  of  high  mountains. 

Because  bright  metal  does  not  absorb  heat,  but  re- 
flects it  ;  and  (as  the  heat  is  thrown  off  from  the  sur- 
face of  'bright  metal  by  reflection)  therefore  a  new  ket- 
tle takes  a  longer  time  to  boil. 

Reflects  heat  —  that  is,  throws  it  off. 

1135  Why  do  persons  wear  white  dresses  in  summer-time  f 

Because  white  throws  off  the  heat  of  the  sun  by  re- 
flection, and  is  a  very  bad  absorbent  of  heat  ;  in  con- 
sequence of  which  wrhite  dresses  never  become  so  hot 
from  the  scorching  sun  as  dark  colors  do. 

1136  Why  do  persons  not  wear  white  dresses  in  winter-time  ? 

Because  white  will  not  absorb  heat  like  black  and 
other  dark  colors  ;  and  therefore  white  dresses  are  not 
so  warm  as  dark  ones. 


Why  are  shoes  hotter  for  being  dusty  f 

Because  dull,  dusty  shoes  will  absorb  heat  from  the 
sun,  earth,  and  air  ;  but  shoes  brightly  polished  throw 
off  the  heat  of  the  sun  by  reflection. 

1138  Why  do  not  the  solar  rays,  even  in  the  hottest  day,  melt  the  snow 
upon  the  tops  of  high  mountains,  which  are  nearer  to  the  sun  than  tlie  kvel 
portions  of  the  earth  ? 

Because  they  only  heat  those  bodies  which  can  alt- 
sorb  their  warmth,  as  the  rough  surface  of  the  earth. 
The  snow  is  indeed  struck  by  the  rays  of  the  sun,  but 
being  a  white  and  shining  body,  it  reflects  them,  and 
remains  cold. 

1139  Why  does  it  always  freeze  on  the  top  of  a  high  mountain  ? 

1.  Because  air  is  heated  by  contact  with  the  earth's 
surface  more  than  by  solar  rays  which  pass  through  it  : 
as  a  mountain-top  affords  very  small  surface  for  such 
contact,  it  remains  intensely  cold  ;  and 

2.  When  air  flows  up  the  side  of  a  mountain,  it  ex- 
pands from   diminished   pressure  ;   and  consequently 
absorbs  heat  from  surrounding  objects. 

Karefied  air  can  hold  more  latent  heat  than  dense  air  can. 

11SO  What  is  the  difference  between  conducting  heat  and  absorbing 
heat? 

To  conduct  heat  is  to  transmit  it  from  one  body  to 


SCIENCE   OF   COMMON   THINGS.  173 

Conduction  of  heat.  How  fanning  cools. 

another  through  a  conducting  medium.     To  absorb  heat 
is  to  suck  it  up,  as  a  sponge  sucks  up  water. 

1131   Give  me  an  example  ? 

Black  cloth  absorbs,  but  does  not  conduct  heat  /  thus, 
if  black  cloth  be  laid  in  the  sun,  it  will  absorb  the  rays 
very  rapidly ;  but  if  one  end  of  the  black  cloth  be 
made  hot,  it  wrould  not  conduct  the  heat  to  the  other 
end. 

113S  Are  good  conductors  of  heat  good  absorbers  also  f 

No ;  every  good  conductor  of  heat  is  a  lad  absorber 
of  it ;  and  no  good  absorber  of  heat  can  be  a  good  con- 
ductor also. 

1133  Is  iron  a  good  absorber  of  heat  f 

No ;  iron  is  a  good  conductor,  but  a  very  bad  ab- 
sorber of  heat. 

1134  If  a  piece  of  brown  paper  be  submitted  to  the  action  of  a  burning- 
glass  it  will  catch  fire  much  sooner  than  a  piece  of  white  paper  would :  ex- 
plain the  reason. 

Because  white  paper  reflects  the  rays  of  the  sun.  or 
throws  them  back  ;  in  consequence  of  which  it  appears 
more  luminous,  but  is  not  so  much  heated  as  dark 
brown  paper,  which  absorbs  the  rays,  and  readily  be- 
comes heated  to  ignition. 

1135  How  does  the  ceaseless  change  of  air  tend  to  decrease  the  warmth 
of  a  naked  body  ? 

The  air  (which  cases  the  body)  absorbs  as  much  heat 
from  it  as  it  can,  while  it  remains  in  contact ;  bein^ 
then  blown  away,  it  makes  room  for  a  fresh  coat  of 
air,  which  readily  absorbs  more  heat. 

Use  Does  the  air  which  encases  a  naked  body  become  (by  contact)  as 
warm  as  the  body  itself? 

It  would  do  so,  if  it  remained  motionless  ;  but,  as  it 
remains  only  a  very  short  time,  it  absorbs  as  much  heat 
as  it  can  in  the  time,  and  passes  on. 

1137*   Why  does  fanning  the  face  in  summer  make  it  cool  f 

Because  the  fan  puts  the  air  in  motion,  and  makes 
it  pass  more  rapidly  over  the  face  ;  and  (as  the  tem- 
perature of  the  air  is  usually  lower  than  that  of  the 

8* 


174  SCIENCE   OF   COMMON    THINGS. 

Wind  generally  feels  cool  Utility  of  black  kettles. 

liumtmface)  each  volume  of  air  carries  off  some  portion 
of  its  heat. 

1138  Does  a  fan  cool  the  air  f 

No  ;  it  makes  the  air  hotter  by  imparting  to  it  the 
heat  out  of  our  face  /  but  it  cools  our  face  by  transfer- 
ring its  heat  to  the  air. 

1139  How  does  fanning  the  face  increase  the  heat  of  the  air  f 

By  driving  the  air  more  rapidly  over  the  human 
body,  and  causing  it,  consequently,  to  absorb  more  heat. 

1140  If  fanning  makes  the  air  hotter,  why  can  it  make  a  person  feel 
cooler  f 

Because  it  takes  the  heat  out  of  the  face,  and  gives 
it  to  the  air. 


Why  does  wind  generally  feel  cool  f 

Because  it  drives  the  air  more  rapidly  over  our  body, 
and  this  rapid  change  of  air  draws  off  a  large  quantity 
of  heat. 

114S    Why  does  air  absorb  heat  more  quickly  by  being  set  in  motion  f 

Because  every  fresh  gust  of  air  absorbs  a  fresh  por- 
tion of  heat  ;  and  the  more  rapid  the  succession  of 
gusts,  the  greater  will  be  the  quantity  of  heat  absorbed. 

1143  If  the  air  were  hotter  than  our  body  would  the  wind  feel  cool  f 

No  ;  the  air  would  feel  insufferably  hot,  if  it  were 
hotter  than  our  body. 

1144  Why  would  the  air  feel  intensely  hot,  if  it  were  warmer  than  our 
body  f 

Because  it  would  add  to  the  heat  of  our  body,  instead 
of  diminishing  it. 

1145  Is  the  air  ever  as  hot  as  the  human  body  f 

In  the  extreme  of  summer  the  temperature  of  the 
air  sometimes  exceeds  the  natural  temperature  of  the 
body  ;  and  when  that  is  the  case,  the  heat  is  almost 
insupportable. 

1146  Why  does  a  kettle  boil  faster  when  the  bottom  and  sides  are 
fovered  wiih  soot  f 

Because  the  black  soot  absorbs  heat  very  quickly  from 
the  fire,  and  the  metal  conducts  it  to  the  water. 


SCIENCE   OF   COMMON   THINGS.  175 

Colors  most  suitable  for  dresses.  Why  a  negro  never  sunburns. 

1147*  Why  do  we  wear  white  linen  and  a  black  outer  dress,  if  we  want 
to  be  warm  f 

Because  the  black  outer  dress  quickly  absorbs  heat 
from  the  sun ;  and  the  white  linen  (being  a  bad  absorb- 
ent) abstracts  no  heat  from  the  warm  body. 

1148  What  colors  are  warmest  for  dresses? 

For  outside  garments  black  is  the  warmest,  and  then 
such  colors  as  approach  nearest  to  black  (as  dark  blue 
and  green).  White  is  the  coldest  color  for  external 
clothing. 

1149  Why  are  dark  colors  (for  external  wear)  so  much  warmer  than 
light  ones  f 

Because  dark  colors  absorb  heat  from  the  sun  more 
abundantly  than  light  ones. 

1150  How  can  you  prove  that  dark  colors  are  warmer  than  light  ones  ? 

If  a  piece  of  black  and  a  piece  of  white  cloth  were 
laid  upon  snow,  in  a  few  hours  the  black  cloth  will 
have  melted  the  snow  beneath  /  whereas  the  white  cloth 
will  have  produced  little  or  no  effect  upon  it  at  all. 

The  darker  any  color  is,  the  warmer  it  is,  because  it  is  a  better  absorb- 
ent of  heat.  The  order  may  be  thus  arranged :  1,  black  (warmest  of  all)  ; 
2,  violet ;  3,  indigo ;  4,  blue ;  5,  green ;  6,  red ;  7,  yellow ;  and  8,  white 
(coldest  of  all). 

1151  Why  does  the  black  skin  of  a  negro  never  sunburn  or  blister  with 
Hie  hot  sun? 

Because  the  black  color  absorbs  the  heat,  conveys  it 
below  the  surface  of  the  skin,  and  converts  it  into  sen- 
sible heat  and  perspiration. 

1153  Why  does  the  white  European  skin  blister  and  burn  when 
exposed  to  the  hot  sun  f 

Because  white  will  not  absorb  heat ;  and  therefore  the 
hot  sun  rests  on  the  surface  of  the  skin^.  and  burns  it. 

1153  Why  do  most  of  the  animals  inhabiting  the  frigid  zones  have 
white  fur,  hair,  or  feathers? 

Because  white  radiates  and  absorbs  but  little  heat. 

1154  What  relation  exists  between  the  power  of  bodies  to  absorb  and 
communicate  heat? 

Those  bodies  which  absorb  heat  freely,  also  part  with 
it  most  rapidly  /  that  is,  they  are  sooner  heated  and 
more  speedily  cooled  than  other  bodies. 


176  SCIENCE   OF    COMMON   THINGS. 

Temperature  of  scalding  water.  General  effects  of  heat. 

1155  At  what  temperature  do  metals  burn  when  handled  f 

Metals  cannot  be  handled  when  raised  to  a  tempe- 
ratnre  of  more  than  one  hundred  and  twenty  degrees. 

1156  At  what  temperature  does  water  scald 7 

At  one  hundred  and  fifty  degrees. 

1157  To  what  extent  can  the  human  system  sustain  the  influence  of 
heated  air  f 

Workmen  enter  ovens,  in  the  manufacture  of  moulds 
of  plaster  of  Paris,  in  which  the  thermometer  stands 
100°  above  the  temperature  of  boiling  water,  and  sustain 
no  injury. 

If  the  person  so  entering  a  heated  oven  should  hold  next  to  his  skin  a 
piece  of  metal,  the  latter  would  absorb  heat  with  sufficient  rapidity  to 
burn  the  surface  with  which  it  was  in  contact. 

1158  Why  is  there  so  great  a  difference  between  the  burning  tempera- 
ture of  'metals  and  air  f 

The  metals  absorb  heat  quickly,  and  part  with  it 
freely ;  the  air  absorbs  heat  very  slowly,  and  does  not 
readily  part  with  it. 

1159  What  class  of  bodies  allow  heat  to  pass  freely  through  them,? 

Transparent  bodies  of  little  density,  as  the  air,  the 
various  gases,  etc.,  etc. 


CHAPTEE   VII. 

EFFECT    OF    HEAT. 
116  O   What  effect  has  heat  upon  substances  generally  f 

It  expands  them,  or  enlarges  their  dimensions. 

1161  Are  the  dimensions  of  every  kind  of  matter  regulated  by  heatf 

They  are;  its  increase,  with  few  exceptions,  separates 
the  particles  of  bodies  to  a  greater  distance  from  each 
other,  producing  expansion,  so  that  the  same  quantity 


SCIENCE   OF  COMMON   THINGS.  177 

Form  of  bodies  dependent  on  heat.  Heat  expands  all  matter. 

of  matter  is  thus  made  to  occupy  a  larger  space  ;  the 
diminution  of  heat  has  an  opposite  effect. 

The  expansion  of  solids  by  heat  is 
clearly  shown  by  the  following  experi- 
ment, Fig.  40 :  m  represents  a  ring  of 
metal,  through  which,  at  the  ordinary 
temperature,  a  small  iron  or  copper 
ball,  a,  will  pass  freely,  this  ball  being  a 
little  less  than  the  diameter  of  the  ring. 
If  this  ball  be  now  heated  by  the  flame 
of  an  alcohol  lamp,  it  will  become  so 
far  expanded  by  heat  as  no  longer  to 
pass  through  the  ring. 

116J3  Is  Hie  form  of  bodies  depend- 
ent on  heat ? 

It  is. 

1163  Sow  is  this  shown  ? 

By  the  increase  of  heat,  solids  are  converted  into 
liquids,  and  liquids  are  dissipated  into  vapor  ;  by  its 
decrease,  vapors  are  condensed  into  liquids,  and  these 
become  solid. 

1164  If  matter  ceased  to  be  influenced  by  heat,  what  would  be  the  effect? 

All  liquids,  vapors,  and  doubtless  even  gases,  would 
become  permanently  solid,  and  all  motion  on  the  sur- 
face of  the  earth  would  be  arrested. 

1165  What  are  the  three  most  apparent  effects  of  heat,  so  far  as  relates 
to  the  form  and  dimensions  of  bodies  ? 

Expansion,  liquefaction,  and  vaporisation. 

1166  Does  heat  expand  air  f 

Yes ;  if  a  bladder  (partially  filled  with  air)  be  tied 
up  at  the  neck,  and  laid  before  the  fire,  the  air  will 
expand  till  the  bladder  bursts. 

1167  Why  will  the  air  swell  if  the  bladder  be  Md  before  the  fire  f 

Because  the  heat  of  the  fire  will  drive  the  particles 
of  air  apart  from  each  other,  and  cause  them  to  occupy 
more  room  than  they  did  before. 

116S  Does  heat  expand  all  matter  ? 

Yes ;  every  thing  (that  man  is  acquainted  with)  is 
expanded  by  heat. 

1169  How  can  we  prove  that  solids  expand  with  heat  f 


178  SCIENCE   OF   COMMON    THINGS. 

Force  of  expansion.  Ice,  why  lighter  than  water. 

If  we  take  the  exact  dimensions  in  length,  breadth, 
and  thickness  of  any  substance  when  cold,  and  measure 
it  again  when  strongly  heated,  it  will  be  found  to  have 
increased  in  every  direction. 

117*O  Do  bodies  expand  with  the  increase  of  heat,  and  contract  upon  its 
withdrawal,  with  any  degree  of  force  f 

Yes ;  the  force  with  which  bodies  contract  and  ex- 
pand under  the  influence  of  heat  is  apparently  iwesist- 
ible,  and  is  recognised  as  one  of  the  greatest  forces  in 
nature. 

117*1  What  peculiarity  exists  in  the  effect  of  heat  upon  the  bulk  of  so^* 
fluids  ? 

That  at  a  certain  temperature  increase  of  heat  causes 
them  to  contract,  and  its  diminution  makes  them  ex- 
pand. 

117*3    What  classes  of  liquids  exhibit  this  peculiarity  f 

Those  only  which  increase  in  bulk  in  passing  from 
the  liquid  to  the  solid  state^  and  this  change  is  remarked 
only  within  a  few  degrees  of  temperature  above  their 
point  of  congelation. 

117*3  What  is  a  noted  example  of  this  exception  to  the  general  laios  of 
Jieat? 

Water  /  ice  swims  upon  the  surface  of  water,  and 
therefore  must  be  lighter,  a  convincing  proof  that  wa- 
ter in  the  act  of  freezing  must  expand. 

117*4  Why  is  the  ice  produced  ly  the  freezing  of  sea  water  ahvays 
fresh  and  free  from  salt  ? 

Because  water,  in  freezing,  if  in  sufficient  quantity 
to  allow  freedom  of  motion  to  its  particles,  expels  all 
impurities  and  coloring  matters. 

117*5  If  a  solution  of  indigo  be  frozen,  why  will  the  ice  formed  be  clear 
and  colorless  f 

Because  the  water  in  which  the  indigo  was  dissolved 
expels  all  the  blue  coloring  matter  while  freezing. 

117*6   Why  are  blocks  of  ice  generally  filled  with  air-bubbles  f 

Because  the  water,  during  the  act  of  freezing,  expels 
the  air  contained  in  it,  and  many  of  the  liberated  bub- 
bles become  lodged  and  imbedded  in  the  thickening 
fluid. 


SCIENCE   OP   COMMON   THINGS.  179 

Cause  of  wcuthcr-worn  rocks.  Cause  of  icicles.  "What  is  ice  f 

IIT*  7  Is  the  force  created  by  the  expansion  of  water  in  the  act  of  freezing 
very  great? 

Yes ;  as  an  illustration  the  following  experiment 
may  be  quoted  :  Cast-iron  bomb-shells,  thirteen  inches 
in  diameter  and  two  inches  thick,  were  filled  with  wa- 
ter, and  their  apertures  or  fuse-holes  firmly  plugged 
with  iron  bolts.  Thus  prepared,  upon  exposure  to  the 
severe  cold  of  a  Canadian  winter,  about  19°  below 
"  zero,"  at  the  moment  the  water  froze,  the  iron  plugs 
were  violently  thrust  out,  and  the  ice  protruded,  and 
in  some  instances  the  shells  burst  asunder,  thus  demon- 
strating the  enormous  interior  pressure  to  which  they 
were  subjected  by  water  assuming  the  solid  state. 

117*8  What  is  the  principal  cause  of  the  rounded  and  weather-worn 
aspect  of  some  rocks,  especially  the  limestone  and  sandstone  rocks  ? 

The  expansion  of  freezing  water  :  water  is  absorbed 
into  their  fissures  and  pores  by  capillary  attraction, 
and  when  it  freezes  during  winter,  it  expands  and  de- 
taches successive  fragments,  so  that  the  original  sharp 
and  abrupt  outline  is  gradually  rounded  and  softened 
down. 

117*9  Why,  in  the  winter,  do  we  let  the  water  run  to  prevent  its  freezing 
in  the  service  pipe  ? 

Because  the  motion  of  the  water  prevents  the  crys- 
tals of  ice  from  forming  or  attaching  themselves  to  the 
sides  of  the  pipe. 

1180  Can  a  lens  be  made  of  ice  capable  of  concentrating  the  rays  of  the 
sun  with  sufficient  intensity  to  inflame  substances  ? 

Yes ;  a  burning-lens  can  be  formed  of  transparent 
ice,  of  power  sufficient  to  produce  effects  nearly  equal 
to  those  of  the  glass  lens. 

1181  What  is  "  ground  ice,"  or  "  anchor  ice  ?" 

Ice  formed  at  the  bottom  of  streams  or  rivers. 

1183   Upon  what  does  the  formation  of  icicles  depend  ? 

Upon  the  successive  congelation  of  drops  or  slender 
streams  of  water. 

1183   What  is  ice  t 

Frozen  water.     "When  the  temperature  of  water  un- 


180  SCIENCE   OF   COMMON   THINGS. 

Expansion  of  water  in  freezing. 

der  ordinary  circumstances  is  reduced  to  32°  of  heat, 
water  will  no  longer  remain  in  a  fluid  state. 

118-4  Can  water  be  cooled  below  32°,  under  any  circumstances,  without 
freezing  f 

If  pure,  recently-boiled  water,  be  cooled  very  slowly 
and  kept  very  tranquil,  its  temperature  may  be  low- 
ered to  21°  without  the  formation  of  ice  ;  but  the  least 
motion  causes  it  to  congeal  suddenly,  and  its  tempera- 
ture rises  to  32°. 

1185    Why  is  solid  ice  lighter  than  water  ? 

Because  water  expands  by  freezing  ;  and  as  its  bulk 
is  increased,  its  specific  gravity  must  be  less. 

Nine  cubic  inches  of  water  become  ten  when  frozen. 

118S  Why  are  earthen  or  porcelain  water  vessels  apt  to  break  in  a 
frosty  night  ? 

Because  the  water  in  them  freezes,  and  (expanding 
by  frost)  bursts  the  vessels  to  make  room  for  its  increas- 
ed volume. 

1187  Why  does  it  not  expand  upwards  (like  boiling  water)  and  run 
over? 

Because  the  surface  is  frozen  first ;  and  the  frozen 
surface  acts  as  a  plug ,  which  is  more  difficult  to  burst 
than  the  earthen  vessel  itself. 

1188  Why  do  tiles,  stones,  and  rocks  often  split  in  winter  f 

Because  the  moisture  in  them  freezes,  and  (expand- 
ing by  frost)  splits  the  solid  mass. 

1180  In  winter-time,  footmarks  and  wheel-ruts  are  often  covered  with 
an  icy  netivork,  through  the  interstices  of  which  the  soil  is  clearly  seen  :  why 
does  the  water  freeze  in  the  form  of  network  f 

Because  it  freezes  first  at  the  sides  of  the  footprints  ; 
other  crystals  gradually  shoot  across,  and  would  cover 
the  whole  surface,  if  the  earth  did  not  absorb  the  water 
before  it  had  time  to  freeze. 

110  O  In  winter-time,  these  footmarks  and  wheel-ruts  are  sometimes 
covered  with  a  perfect  sheet  of  ice,  and  not  an  icy  network :  why  is  this  f 

Because  the  air  is  colder  and  the  earth  harder  than 
in  the  former  case  ;  in  consequence  of  which  the  entire 
surface  of  the  footprint  is  frozen  over  before  the  earth 
has  had  time  to  absorb  the  water. 


SCIENCE   OF  COMMON   THINGS.  181 

Water-pipes  often  burst  in  winter.  Bottom  of  a  river  rarely  frozen. 

1191  Why  is  not  the  ice  solid  in  these  ruts  ? — why  is  there  only  a  very 
thin  film  or  network  of  ice  ? 

Because  the  earth  absorbs  most  of  the  water,  and 
•leaves  only  the  icy  film  behind. 

1193    Why  do  water-pipes  frequently  burst  in  frosty  weather? 

Because  the  water  in  them  freezes,  and  (expanding 
by  frost)  bursts  the  pipes  to  make  room  for  its  increased 
volume. 

1193  Why  does  the  earth  crack  in  intense  cold  weather  ? 

The  moisture  in  the  soil  in  the  act  of  freezing  ex- 
pands^ and  forces  the  particles  asunder.  The  disrup- 
tion of  the  earth  is  frequently  accompanied  with  a  loud 
sound. 

1194  Does  not  water  expand  by  heat  as  well  as  ly  coldf 

Yes ;  it  expands  as  soon  as  it  is  more  than  42°,  till  it 
boils  /  after  which  time  it  flies  off  in  steam. 

1195  When  does  water  begin  to  expand  from  cold? 

Yvrhen  it  is  reduced  to  40°.  Water  is  wisely  ordained 
to  be  an  exception  to  a  very  general  rule  :  it  contracts 
till  it  is  reduced  to  40°,  and  then  it  expands  till  it 

freezes. 

The  general  rule  is  this : — That  cold  condenses  and  contracts  the  volume 
of  nearly  everything;  but  .water  is  not  contracted  by  cold  when  it  freezes 
(which  it  does  at  32°). 

1196  Why  does  water  expand  when  it  freezes  $ 

The  expansion  of  water  at  the  moment  of  freezing  is 
attributed  to  a  new  and  peculiar  arrangement  of  its 
particles.  Ice  is,  in  reality,  crystallized  water,  and  dur- 
ing its  formation  the  particles  arrange  themselves  in 
ranks  and  lines  which  cross  each  other  at  angles  of  60° 
and  120°,  and  consequently  occupy  more  space  than 
when  liquid.  This  may  be  seen  by  examining  the  sur- 
face of  water  in  a  saucer  while  freezing. 

1197'   Why  is  the  bottom  of  a  river  rarely  frozen  f 

Because  water  ascends  to  the  surface  as  soon  as  it  be- 
comes colder  than  42°,  aad  (if  it  freezes)  floats  there  till 
it  is  melted. 

1198  Show  the  wisdom  of  the  Creator  in  this  wonderful  exception  to  a 
general  law. 


182  SCIENCE   OF   COMMON  THINGS. 

Why  -water  freezes  first  at  the  surface.  Why  running  water  freezes  slowly. 

If  ice  were  heavier  than  water  it  would  sink,  and  a 
river  w^ould  soon  become  a  solid  Hock  of  ice,  which 
could  never  be  dissolved. 

The  general  rule  is,  that  all  substances  become  heavier  from  condensa- 
tion ;  but  ice  is  lighter  than  water. 

1199  Why  does  not  the  ice  on  the  surface  of  a  river  chill  the  water 
beneath,  and  make  it  freeze  f 

1.  Because  water  is  a  very  bad  conductor ',   and  is 
heated  or  chilled  by  convection  only ; 

2.  If  the  ice  on  the  surface  were  to  communicate  its 
coldness  to  the  water  beneath,  the  water  beneath  would 
communicate  its  heat  to  the,  ice.  and  the  ice  would  in- 
stantly melt  /  and 

3.  The  ice  on  the  surface  acts  as  a  shield,  to  prevent 
the  cold  from  penetrating  through  the  river  to  freeze  the 
water  below  the  surface. 

1500  Why  does  water  freeze  at  the  surface  first? 

Because  the  surface  is  in  contact  with  the  air,  and  the 
ftir  carries  away  its  heat. 

1501  Why  does  the  coat  of  ice  grow  tiiicker  and  thicker  if  the  frost 
continues  f 

Because  the  heat  of  the  water  (immediately  below 
the  frozen  surface)  passes  through  the  ice  into  the  cold 
air. 

1SOS  Why  are  not  whole  rivers  frozen  (layer  ly  layer)  till  they  be- 
come solid  icef 

Because  water  is  so  slow  a  conductor,  that  our  frosts 
never  continue  long  enough  to  convert  a  whole  river 
into  a  solid  mass  of  ice. 

12O3   Why  does  not  running  water  freeze  as  fast  as  still  water  f 

1.  Because  the  motion  of  the  current  disturbs  the 
crystals,  and  prevents  their 'forming  into  a  continuous 
surface  ;  and 

2.  The  heat  of  the  under  surface  is  communicated  to 
the  upper  surface  by  the  motion  of  the  water. 

1SO4  When  running  water  is  frozen,  why  is  the  ice  generally  very 
rough f 

Because  little  flakes  of  ice  are  first  formed  and  carried 
down  the  stream,  till  they  meet  some  obstacle  to  stop 


SCIENCE    OF   COMMON   THINGS.  183 

Sea  water  is  rarely  frozen.  How  the  depth  of  water  influences  freezing. 

them ;  other  flakes  of  ice  (impinging  against  them)  are 
arrested  in  like  manner  ;  and  the  edges  of  the  different 
flakes  overlapping  each  other,  make  the  surface  rough. 

13O5    Why  do  some  parts  of  a  river  freeze  less  tlian  others  ? 

Because  springs  issue  from  the  bottom,  and  (as  they 
bubble  upwards)  thaw  the  ice,  or  make  it  thin. 

13O0    When  persons  fall  into  a  river  in  winter-time,  why  does  the  water 
feel  remarkably  warm  1 

Because  the  frosty  air  is  at  least  ten  or  twelve  de- 
grees colder  than  the  water  is. 

The  water  below  the  surface  is  at  least  42°,   but  the  air  32°,  or  even 
less.         ' 

1207    Why  is  sea  water  rarely  frozen  1 

1.  Because  the  mass  of  water  is  so  great,  that  it  re- 
quires a  very  long  time  to  cool  the  whole  volume  down 
to  forty  degrees  ; 

2.  The  ebb  and  flow  of  the  sea  interfere  with  the 
cooling  influence  of  the  air  ;  and 

3.  Salt  water  never  freezes  till  the  surface  is  cooled 
down  to  twenty-seven  degrees,  or  five  degrees  below  the 
freezing  point  of  fresh  water. 

13O3    Why  do  some  lakes  rarely  (if  ever)  freeze?  f 


1.  Because  they  are  very  deep  ;  and 

2.  Because  their  water  is  supplied  by 


springs  which 
bubble  from  the  bottom. 

ISO 9  How  does  the  depth  of  water  influence  its  freezing  1 

It  is  necessary  that  the  whole  volume  of  water  should 
be  reduced  to  forty  degrees  before  the  surface  will 
begin  to  freeze  ;  and  the  deeper  the  water,  the  longer  it 
will  be  before  the  whole  volume  is  thus  reduced. 

1310  Why  do  springs  at  the  bottom  of  a  lake  prevent  its  freezing  ? 

Because  they  keep  continually  sending  forth  water 
having  a  temperature  above  that  of  the  mass  of  the 
water,  which  prevents  the  lake  from  being  reduced  to 
the  necessary  degree  of  coldness. 

1311  It  is  more  chilly  in  a  thaw  than  in  a  frost :   explain  the  reason 
of  this. 

When  froz3n  water  is  thawed,  it  absorbs  heat  from 


184  SCIENCE  OF  COMMON  THINGS. 

Why  it  is  chilly  during  a  thaw.  Cause  of  hoar-frost. 

the  air,  etc.,  to  melt  the  ice  ;  in  consequence  of  which 
the  heat  of  the  air  is  greatly  reduced. 

1212  To  what  extent  can  the  temperature  be  reduced  by  the  liquefaction 
of  a  mixture  of  the  two  solids,  snow  and  salt  ? 

By  means  of  a  mixture  of  equal  weights  of  common 
salt  and  fresh  snow  (or  pounded  ice),  a  steady  temper- 
ature of  nearly  40°  below  the  freezing  point  of  water 
can  be  maintained  for  hours. 

1213  How  much  heat  is  required  to  melt  ice  f 

The  conversion  of  a  cube  of  ice,  three  feet  on  the 
side,  into  water  at  32°,  would  absorb  all  the  heat  pro- 
duced by  the  combustion  of  a  bushel  of  coal. 

1214  Why  does  the  frost  of  winter  make  the  earth  in  spring  loose  and 
friable  f 

Because  the  water  absorbed  by  the  earth  in  warm 
weather,  expanding  by  the  frost,  thrusts  the  particles 
of  earth  apart  from  each  other,  and  leaves  a  chink  or 
crack  between. 

1215  Show  the  wisdom  of  the  Creator  in  this  arrangement. 

These  cracks  in  the  earth  let  in  air,  dew,  rain,  and 
many  gases  favorable  to  vegetation. 

1216  Why  are  delicate  trees  covered  with  straw  in  winter  f 

Because  straw  (being  a  non-conductor)  prevents  the 
sap  of  the  tree  from  being  frozen. 

1217  What  is  hoarfrost  f 

There  are  two  sorts  of  hoarfrost :  1.  Frozen  dew  ;  and 
2.  Frozen  fog. 

1218  What  is  the  cause  of  the  ground  hoarfrost,  or  frozen  dew  ? 

Yery  rapid  radiation  of  heat  from  the  earth  ;  in 
consequence  of  which  the  surface  is  so  cooled  down, 
that  \\,  freezes  the  dew  condensed  upon  it. 

1219  Why  is  hoarfrost  seen  only  after  a  very  clear  night  ? 

Because  the  earth  will  not  have  thrown  off  heat 
enough  by  radiation  io  freeze  the  vapor  condensed  upon 
its  surface,  unless  the  night  be  very  clear  indeed. 

1220  What  is  the  cause  of  that  hoarfrost  which  arises  from  frozen  fog  f 


SCIENCE   OF   COMMON   THINGS.  185 

Where  hoar-frost  does  not  accumulate.  Frostwork  on  windows. 

The  thick  fog  which  invested  the  earth  during  the 
night  (being  condensed  by  the  cold  frost  of  early  morn- 
ing) is  congealed  upon  every  object  with  which  it  comes 
in  contact. 

1221    Why  is  there  little  or  no  hoarfrost  under  shrubs  and  shady  trees  f 

1.  Because  the  leafy  top  arrests  the  process  of  radi- 
ation from  the  earth  ;  and 

2.  Shrubs  and  trees  radiate  heat  towards  the  earth ; 
and  therefore  the  ground  beneath  is  rarely  cold  enough 
to  congeal  the  little  dew  which  rests  upon  it. 

1SSS  Why  does  hoarfrost  very  often  cover  the  ground  and  trees,  when 
the  water  of  rivers  is  not  frozen  ? 

Because  it  is  not  the  eifect  of  cold  in  the  air,  but 
cold  on  the  surface  of  the  earth  (produced  by  excessive 
radiation),  which  freezes  the  dew  condensed  upon  it. 

1223  Why  is  the  hoarfrost  upon  grass  and  vegetables  much  thicker 
than  that  upon  lofty  trees  ? 

Because  the  air  (resting  on  the  surface  of  the  ground) 
is  much  colder  after  sunset  than  the  air  higher  up  •  in 
consequence  of  which  more  vapor  is  condensed  and 
frozen  there. 

1224  What  is  the  cause  of  the  pretty  frostwork  seen  on  bedroom  win- 
dows in  winter-time? 

The  breath  and  insensible  perspiration  of  the  sleeper 
(coming  in  contact  wTith  the  ice-cold  window)  2x0, frozen 
by  the  cold  glass,  and,  crystallizing,  form  those  beautiful 
appearances  seen  on  a  winter  morning. 

1225  Are  all  the  figures  of  frostwork  formed  in  accordance  ivith  certain 
fixed  laws  ? 

All  these  figures  are  limited  ~by  certain  laws,  and  the 
lines  which  bound  them  form  among  themselves  no 
angles  but  those  of  30°,  60°,  and  120°. 

1226  If  you  fracture  thin  ice  by  allowing  a  pole  or  weighi  to  fall  upon 
it,  will  the  lines  of  the  fracture  have  anything  of  regularity  ? 

Yes  ;  the  fracture  will  generally  present  a  star  with 
six  equidistant  radii,  or  angles  of  60°. 

122 7  Why  is  a  glass  or  earthen  vessel  apt  to  break  when  hot  water  is 
poured  into  itf 

Because  the  inside  of  the  glass  is  expanded  by  the 


186  SCIENCE    OF   COMMON    THINGS. 

Why  glass  breaks  when  placed  in  hot  water.  "Why  a  stove  snaps. 

hot  water,  and  not  the  outside  /  so  tlie  glass  snaps  in 
consequence  of  this  unequal  expansion. 

•1338    Why  is  not  the  outside  of  the  glass  expanded  by  the  hot  water  as 
well  as  the  inside  ? 

Because  glass  is  a  bad  conductor  of  heat,  and  breaks 
before  the  heat  of  the  inner  surface  is  conducted  to  the 
outside. 

1339  Why  does  a  glass  snap  because  the  inner  surface  is  hotter  than 
the  outer  ? 

Because  the  inner  surface  is  expanded,  and  not  the 
outer  ;  in  consequence  of  which  an  opposing  force  is 
created  which  breaks  the  glass. 

1330  Why  does  a  cooper  heat  his  hoops  red  hot  when  he  puts  them  on 
a  tub? 

1.  As  iron  expands  by  heat,  the  hoops  will  be  larger 
when  they  are  red  hot  ;  in  consequence  of  which  they 
wTill  fit  on  the  tub  more  easily  ;  and 

2.  As  iron  contracts  by  cold,  the  hoops  wrill  shrink 
as  they  cool  down,  and  girt  the  tub  with  a  tighter 
grasp. 

1331  Why  does  a  wheelwright  make  the  tire  red  hot  which  he  fixes  on 
a  wheel  f 


1.  That  it  may^  on  more  easily  •  and 

2.  That  it  may  girt  the  wheel  more  tightly. 

1333  Why  will  the  wheelwrights  tire  Jit  the  wheel  more  easily  for  beiny 
made  red  hot  f 

Because  it  will  be  expanded  by  the  heat,  and  (being 
larger)  will  go  on  the  wheel  more  easily. 

1333  Why  will  the  tire  which  has  been  put  on  hot  girt  the  wheel  more. 
firmly  ? 

Because  it  will  shrink  when  it  cools  down,  and 
therefore  girt  the  wheel  with  a  tighter  grasp. 

1334  Why  does  a  stove  make  a  crackling  noise  when  afire  is  very  hot? 

Because  it  expands  from  the  heat  ;  and  the  parts  of 
the  stove  rulbing  against  each  other,  or  driving  against 
the  bricks,  produce  a  crackling  noise. 

1335  Why  does  a  stove  make  a  similar  crackling  noise  when  a  large 
fire  is  put  out  f 


SCIENCE  OF  COMMON  THINGS.  187 

Why  clocks  go  faster  in  summer  than  in  winter. 

Because  the  metal  of  the  stove  contracts,  by  reason 
of  a  reduction  of  temperature,  when  the  fire  is  extin- 
guished. 

1336  Why  are  the  nails  in  almost  all  old  houses  loose  and  easily 
drawn  out  ? 

Because  the  iron  expands  in  the  summer,  and  con- 
tracts in  the  winter,  more  than  the  stone  or  wood,  and 
thus  the  opening  is  gradually  enlarged  after  a  lapse  of 
time. 

133*7  Why  does  a  piano  give  a  higher  tone  in  a  cold  than  in  a  warm 
room  f 

Because  in  a  cold  room  the  strings  are  contracted 
and  tighter. 

1333    Why  do  clocks  go  slower  in  summer  and  faster  in  winter? 

Because  the  pendulums  elongate  in  summer  through 
the  effects  of  heat,  and  consequently  vibrate  slower ; 
while  in  winter  they  contract,  become  shorter,  and 
vibrate  more  rapidly. 

1339  Hoiu  is  this  inequality  in  the  rate  of  motion  in  timepieces  obviated  f 

By  what  is  called  a  compensating  pendulum  /  that 
is,  one  constructed  of  two  metals,  possessing  different 
expansive  powers,  in  such  a  manner  that  the  greater 
expansion  of  one  bar  in  one  direction  equals  the  less 
expansion  of  other  bars  in  a  different  direction,  and 
thus  maintain  an  invariable  length  of  the  pendulum. 

1340  Does  wood  expand  under  the  influence  of  heat  differently  from 
metal  ? 

Yes ;  an  iron  bar  expands  and  contracts  equally  in 
all  directions,  but  wood  expands  and  contracts  more  in 
breadth  than  in  length. 

134:1  Why  will  a  person,  buying  oil,  molasses,  spirits,  etc.,  by  the  mea- 
sure, get  a  greater  weight  of  the  same  material  in  the  same  measure  in  the 
winter  tiian  in  the  summer  ? 

Because  these  liquids  contract  and  occupy  less  space 
in  the  winter  than  in  summer ;  consequently  it  requires 
more  of  the  same  kind  to  fill  the  same  space  in  winter 
than  in  summer. 

1343  How  can  heat  be  measured  f 

Only  by  its  effects :  since  the  magnitude  of  any  body 


188  SCIENCE   OF   COMMON    THING?. 

What  is  temperature  ?  Thermometers  and  pyrometers. 

changes  with  the  heat  to  which  it  is  exposed  ;  and  since, 
when  subject  to  the  same  calorific  influences,  it  always 
has  the  same  magnitude,  these  dilatations  and  contrac- 
tions, which  are  the  constant  effects  of  heat,  may  be 
taken  as  the  measure  of  the  physical  cause  that  pro- 
duced them. 

1343  What  is  the  temperature  of  a  body  ? 

It  is  the  actual  state  of  a  body  at  any  moment,  deter- 
mined by  a  comparison  of  its  magnitude  with  the  heat 
to  which  it  is  exposed. 

1344  What  is  a  change  of  temperature  f 

The  change  in  magnitude  which  a  body  suffers  by 
changes  in  the  heat  to  which  it  is  exposed. 

1345  What  are  the  instruments  for  measuring  lieat  called? 

Thermometers  and  pyrometers. 

1346  What  is  the  difference  between  them  f 

A  thermometer  is  used  for  measuring  moderate  tem- 
peratures ;  wrhile  the  pyrometer  is  chiefly  applied  to  de- 
termine the  more  elevated  degrees  of  heat. 

1347*  What  substances  are  best  adapted  for  measuring  the  effects  of 
heat  by  their  expansion  and  contraction  f 

Liquids,  above  all  other  substances. 

1348  Why  are  liquids  best  adapted  for  this  purpose  f 

Because  in  solids  the  direct  expansion  by  heat  is  so 
small  as  to  be  seen  or  measured  with  difficulty  ;  in  air 
or  gases  it  is  too  extensive  and  too  liable  to  be  affected 
by  atmospheric  pressure  ;  but  liquids  are  free  from  both 
disadvantages. 

1349  What  liquid  is  generally  used  for  the  construction  of  ordinary 
thermometers  f 

Mercury  or  quicksilver. 

035 O  What  metal  is  distinguished  from  aU  others  by  its  fluidity  at 
ordinary  temperatures  f 

Mercury  or  quicksilver. 

1351  Does  mercury,  like  other  metals,  expand  by  heatf 

It  readily  expands  or  contracts  with  every  variation 
of  temperature. 


SCIENCE   OF   COMMON   THINGS.  189 

Use  of  mercury  in  thermometers.  How  thermometers  are  constructed. 

1353  Why  is  mercury  preferable  to  all  other  liquids  for  the  purposes 
of  the  thermometer  f 

Because  it  'boils  at  a  higher  temperature  than,  any 
other  liquid,  except  certain  oils ;  and,  on  the  other 
hand,  it  freezes  at  a  lower  temperature  than  all  other 
liquids,  except  some  of  the  most  volatile,  such  as  ether 
and  alcohoL 

Thus,  a  mercurial  thermometer  will  have  a  wider  range  than  any  other 
liquid  thermometer.  It  is  also  attended  with  this  convenience,  that  the 
extant  of  temperature  included  between  melting  ice  and  boiling  water- 
stands  at  a  considerable  distance  from  the  limits  of  its  range,  or  its 
freezing  and  boiling  points. 

1253    Of  what  does  the  mercurial  thermometer  consist  f 

The  mercurial  thermometer  consists  essentially  of  a 
glass  tube  with  a  bulb  at  one  extremity,  and  which, 
having  been  filled  with  mercury  at  a  certain  tempera- 
ture, introduced  through  the  open  end,  has  been  her- 
metically sealed  while  full,  so  that  no  air  can  after- 
wards enter  it. 

As  the  tube  and  mercury  in  it  gradually  become  cooled,  the  inclosed 
fluid  contracts,  and  consequently  sinks,  leaving  above  it  a  vacant  space 
or  vacuum,  through  which  it  may  again  expand  on  the  application  of 
heat. 

1354  As   thermometers  are  constructed  of  different  dimensions  and 
capacities,  how  are  they  graduated  to  indicate  the  same  temperature  under 
the  same  circumstances,  as  the  freezing  point,  for  example? 

The  thermometers  are  first  immersed  in  melting  snow 
or  ice.  The  mercury  will  be  observed  to  stop  in  each 
thermometer-tube  at  a  certain  height ;  these  heights 
are  then  marked  upon  the  tubes.  Now  it  has  been 
ascertained  that  at  whatever  time  and  place  the  instru- 
ments may  be  afterwards  immersed  in  melting  snow  or 
ice,  the  mercury  contained  in  them  will  always  fix  itself 
at  the  point  thus  marked.  This  point  is  called  the 
freezing  point  of  water. 

1355  How  is  the  boiling  point  ascertained  ? 

It  has  been  found  that  at  whatever  time  or  place  the 
instruments  are  immersed  in  pure  water,  when  boiling, 
provided  the  barometer  stands  at  the  height  of  thirty 
inches,  the  mercury  will  always  rise  in  each  to  a  certain 

9 


190  SCIENCE   OF   COMMON   THINGS. 

Determination  of  the  boiling  and  freezing  points. 

height.     This,  therefore,  forms  another  fixed  point  on 
the  geometric  scale,  and  is  called  the  boiling  voint. 

1356  How  are  the  intermediate  points  determined  ? 

In  Fahrenheit's  thermometer,  the  intervals  on  the 
scale,  between  the  freezing  and  boiling  points,  are 
divided  into  180  equal  parts.  This  division  is  similarly 
continued  below  the  freezing  point  to  the  place  0,  and 
each  division  upwards  from  that  is  marked  with  the  suc- 
cessive number  1,  2,  3,  etc.  The  freezing  point  will 
now  be  the  32d  division,  and  the  boiling  point  will  be 
the  212th  division.  These  divisions  are  called  degrees, 
and  the  boiling  point  will  therefore  be  212°,  and  the 
freezing  temperature,  32°. 

1557  When  and  by  wham  was  the  thermometer  invented  ? 

The  thermometer  was  invented  about  the  year  1600; 
but,  like  many  other  inventions,  the  merit  of  its  dis- 
covery is  not  to  be  ascribed  to  one  person,  but  to  be 
distributed  among  many. 

1558  Why  is  the  thermometer  in  general  use  in  the  United  States, 
England,  and  Holland,  called  Fahrenheit's  thermometer '? 

Because  thermometers  having  a  like  graduation  were 
first  manufactured  by  Fahrenheit,  a  Dutch  philoso- 
phical instrument-maker.  The  employment  of  mercury 
as  the  most  suitable  fluid  for  the  thermometer  is  also 
usually  attributed  to  him. 

IS 5  9  How  many  kinds  of  tliermorneters 
are  in  general  use  ? 

Three  :  Fahrenheit's,  Reau- 
mur's, and  the  Centigrade  ther- 
mometer, or  thermometer  of 
Celsius. 

126O   What  constitutes  the    di/erence 
letween  these  instruments  f 

The  differences  of  graduation 
between  the  freezing  and  boiling 
points  of  water.  Reaumur  is 
divided  into  eighty  degrees,  the 
Centigrade  into  one  hundred, 
Fig  4L  and  Fahrenheit's  into  one  hun* 


SCIENCE   OF   COMMON   THINGS. 


191 


Different  varieties  of  thermometers. 


Construction  of  pyrometers. 


dred  and  eighty.  According  to  Reaumur,  water  freezes 
at  0°,  and  boils  at  80° ;  according  to  Centigrade,  it 
freezes  at  0°,  and  boils  at  100° ;  and  according  to  Fah- 
renheit, it  freezes  at  32°,  and  boils  at  212°;  the  last,  very 
singularly,  commences  counting  not  at  the  freezing 
point,  but  32°  below  it. 

The  differences  between  these  instruments  can  be  easily  seen  by  refer- 
ence to  Fig.  41. 

1261  In  what  countries  are  the  Reaumur  and  Centigrade  thermometers 
generally  used  ? 

fieaumur  is  in  general  use  in  Germany,  and  the 
Centigrade  in  France  /  but  for  scientific  purposes  the 
Centigrade  is  almost  universally  adopted. 

12362  At  what  temperature  does  mercury  freeze  ? 

At  about  39°  below  the  zero  of  Fahrenheit's  thermo- 
meter. 

1263  How  are  degrees  of  cold  more  intense  than  this  measured  f 

By  using  a  thermometer  filled  with  alcohol  colored 
red,  as  this  fluid  when  pure  does  not  congeal  at  100° 
Fahrenheit  below  zero. 

1264  At  what  temperature  does  mercury  boil  f 

At  660°  Fahrenheit. 

1265  How  are  temperatures  greater  than  this  determined  f 

By  means  of  the  expansion  of  solids  •  and  instru- 
ments founded  upon  this  principle  are  commonly  called 
pyrometers. 


Fig.  42. 
Ihe  construction  of  the  pyrometer  is  represented  in  Fig.  42.     A  repre- 


192  SCIENCE   OF   COMMON   THINGS. 

What  is  liquefaction  1  Why  ice  is  melted  by  heat. 

senta  a  metallic  bar,  fixed  at  one  end,  B,  but  left  free  at  the  other,  and  in 
contact  with  the  end  of  a  pointer,  K,  moving  freely  over  a  graduated  scale. 
If  the  bar  be  heated  by  the  flame  of  alcohol,  the  metal  expands,  and 
pressing  upon  the  end  of  the  pointer  moves  it,  in  a  greater  or  less  degree. 

13  GQ    On  what  principle  have  pyrometers  generally  been  constructed  f 

On  the  relative  expansion  of  bars  of  iron,  or  some 
other  metal. 

12Q7  Does  a  thermometer  inform  us  how  much  heat  any  body  con- 
tains ? 

No ;  it  merely  points  out  a  difference  in  the  tem- 
perature of  two  or  more  substances.  All  we  learn  by 
the  thermometer  is  whether  the  temperature  of  one 
body  is  greater  or  less  than  that  of  another ;  and  if 
there  is  a  difference  it  is  expressed  numerically — 
namely,  by  the  degrees  of  the  thermometer. 

It  must  be  remembered  that  these  degrees  are  parts  of  an  arbitrary 
scale,  selected  for  convenience,  without  any  reference  whatever  to  the 
actual  quantity  of  heat  present  in  bodies. 

1368  After  the  expansion  of  solids,  when  acted  upon  by  heat,  what 
other  effect  is  next  observed  ? 

They  change  their  original  state,  become  liquid,  or 
melt.  Many  of  them  become  soft  before  melting,  so 
that  they  may  be  kneaded ;  for  instance,  wax,  glass, 
and  iron ;  in  this  condition,  glass  can  be  bent  and 
moulded  like  wax,  and  iron  can  be  forged  or  welded. 

13  B9   What  is  meant  by  liquefaction  ? 

The  conversion  of  a  solid  into  a  liquid  by  the  agency 
of  heat,  as  solid  ice  is  converted  into  water  by  the  heat 
of  the  sun. 

137O   Why  is  ice  melted  by  the  heat  of  the  sun  f 

Because,  when  the  heat  of  the  sun  enters  the  solid 
ice,  it  forces  its  particles  asunder,  till  their  attraction 
of  cohesion  is  sufficiently  overcome  to  convert  the  solid 
ice  into  a  liquid. 

13*71   Why  are  metals  melted  by  the  heat  of  fire  f 

Because,  when  the  heat  of  the  fire  enters  the  solid 
metal,  it  forces  its  particles  asunder,  till  their  attraction 
of  cohesion  is  sufficiently  overcome  to  convert  the  solid 
metal  into  a  liquid. 


SCIENCE    OF   COMMON   THINGS.  193 

What  is  a  solution  ?  Why  water  dissolves  sugar. 

IS  7*3  When  salt  is  mixed  with  water  and  disappears  in  the  liquid, 
what  is  said  to  have  taken  place  ? 

The  salt  is  said  to  have  dissolved  in  the  water,  and 
.the  liquid  is  now  a  solution  of  salt. 

IS  73   What,  then,  w  a  solution  f 

A  solution  is  the  result  of  an  attraction  or  affinity 
between  a  solid  and  a  fluid ;  and  when  a  solid  disap- 
pears in  a  liquid,  if  the  compound  exhibits  perfect 
transparency,  we  have  an  example  of  a  perfect  solution. 

1374    When  is  a  solution  said  to  be  saturated  f 

When  the  fluid  has  dissolved  as  much  of  the  solid  as 
it  is  capable  of  doing,  it  is  said  to  be  saturated  ;  or,  in 
other  words,  the  affinity  or  attraction  of  the  fluid  for 
the  solid  continues  to  operate  to  a  certain  point,  where 
it  is  overbalanced  by  the  cohesion  of  the  solid  ;  it  then 
ceases,  and  the  fluid,  is  said  to  be  saturated. 

1S75    What  is  the  difference  between  a  solution  and  a  mixture  f 

A  solution  is  a  chemical  union  /  a  mixture  is  a  mere 
mechanical  union  of  bodies. 

IS  70    Why  will  water  dissolve  sugar  f 

Because  there  is  attraction  or  affinity  between  the 
particles  of  the  water  and  the  particles  of  the  sugar. 

1S77   What  do  we  mean  by  affinity  f 

Affinity  is  that  kind  of  attraction  in  virtue  of  which 
bodies  of  a  dissimilar  character  combine  together  into 
a  whole,  which  appears  perfectly  uniform  to  the  senses, 
even  when  assisted  by  powerful  magnifying  instruments. 

1S7S    Why  will  not  water  dissolve  granite  or  metallic  iron  f 

Because  there  is  not  sufficient  affinity  or  attraction 
between  the  particles  of  the  water  and  those  of  the  iron 
or  granite. 

1379  Are  there  any  liquids  that  have  sufficient  affinity  to  dissolve  iron 
and  granite  ? 

Yes ;  certain  acids  have  so  great  an  affinity  for  the 
iron  and  granite  that  they  are  enabled  to  dissolve  them. 

1S8O    Why  will  not  water  dissolve  oil? 

Because  there  is  no  affinity  or  attraction  between  the 
particles  of  the  two  substances. 


194:  SCIENCE  OF  COMMON  THINGS. 

Vaporization.  Why  heat  converts  water  into  eteam. 

IS  81   Why  will  alcohol  and  ether  dissolve  oil  f 

Because  the  attraction  or  affinity  between  the  alco- 
hol or  ether  and  the  oil  is  sufficient  to  enable  them  to 
effect  a  solution. 

1S8S    What  effect  has  heat  upon  the  dissolving  power  of  liquids! 

In  most  cases  the  addition  of  heat  to  a  liquid  greatly 
increases  its  solvent  properties.  Hot  water  will  dissolve 
much  more  sugar  than  cold  water,  and  hot  water  will 
also  dissolve  many  things  which  cold  water  is  unable 
to  affect. 

1583  Why  does  not  wood  melt  like  metal  ? 

Because  the  heat  of  the  fire  decomposes  the  wood  into 
gas,  smoke,  and  ashes,  and  the  different  parts  separate 
from  each  other. 

1584  What  is  meant  by  vaporization? 

The  conversion  of  a  solid  or  liquid  into  vapor  /  as 
snow  or  water  is  converted  into  vapor  by  the  heat  of 
the  sun. 

IS  85   Why  is  water  converted  into  steam  by  the  heat  of  the  fire  f 

Because,  when  the  heat  of  the  fire  enters  the  water, 
it  separates  its  substance  into  very  minute  particles, 
which  (being  lighter  than  air)  fly  off  from  the  surface 
in  the  form  of  steam. 

1S86    Why  do  doors  swell  in  rainy  weather  ? 

Because  the  air  is  filled  with  vapor,  wrhich  (pene- 
trating into  the  pores  of  the  wood)  forces  its  particles 
farther  apart,  and  swells  the  door. 

1SS7   Why  do  doors  shrink  in  dry  weather? 

Because  the  moisture  is  absorbed  from  the  wood,  and, 
as  the  particles  are  brought  closer  together,  the  size  of 
the  door  is  lessened  /  in  other  words,  the  wood  shrinks. 

1SSS  Why  does  a  drop  of  water  sometimes  roll  along  a  piece  of  hot 
iron  without  leaving  the  least  trace  f 

Because  the  bottom  of  the  drop  is  changed  into  vapor, 
which  buoys  the  drop  up,  without  allowing  it  to  touch 
the  iron. 

1SS9   Whydoesitrott? 


SCIENCE  OF   COMMON   THINGS.  195 

Volatile  substances.  What  is  distillation  ? 

Because  the  current  of  air  (which  is  always  passing 
over  a  heated  surface)  drives  it  along. 

1290  Why  does  a  laundress  put  a  little  saliva  on  aflat-iron  to  know  if 
it  be  hot  enough  ? 

Because  when  the  saliva  sticks  to  the  iron  and  is 
evaporated,  she  knows  it  is  not  sufficiently  hot  ;  but 
when  it  runs  along  the  iron,  it  is. 

1291  Why  is  the  flat-iron  hotter  if  the  saliva  runs  along  it,  than  if  it 
adheres  till  it  is  evaporated? 

Because  when  the  saliva  runs  along  the  iron,  the  heat 
is  sufficient  to  convert  the  bottom  q£  the  drop  into  vapor  • 
but  if  the  saliva  will  not  roll,  the  iron  is  not  sufficiently 
hot  to  convert  the  bottom  of  the  drop  into  vapor. 

1292  To  what  substances  do  we  apply  the  term  "  volatile  ?" 

To  those  which  have  a  great  tendency  to  assume  the 
gaseous  form. 

1293  To  what  substances  do  we  apply  the  term  "fixed,"  or  "non-vola- 
tile?" 

To  those  in  which  the  tendency  to  assume  the  gaseous" 
form  is  small. 

1294  Do  vapors  occupy  much  more  space  tlian  the  substances  from  which 
they  were  produced  f 

They  occupy  a  much  greater  space  ;  water,  in  passing 
from  its  point  of  greatest  density  into  vapor,  expands  to 
sixteen  hundred  and  ninety-six  times  its  volume. 

1295  Under  what  two  heads  does  the  subject  of  vaporization  divide 
itself? 

Into  ebullition  and  evaporation 

1296  What  is  distillation? 

A  process  by  which  one  body  is  separated  from  an- 
other by  means  of  heat,  in  cases  where  one  of  the  bodies 
assumes  the  form  of  vapor  at  a  lower  temperature  than 
the  other ;  this  first  rises  in  the  form  of  vapor,  which  is 
received  and  condensed  in  a  separate  vessel. 

1297*  How  is  the  process  of  simple  distillation  effected  ? 

A  peculiar-shaped  vessel  called  a  retort  (Fig.  43)  is 
half  filled  with  a  volatile  liquid  and  heated ;  the  steam, 
as  it  forms,  passes  through  the  neck  of  the  retort  into  a 


196  SCIENCE   OF   COMMON   THINGS. 

"Why  distilled  water  Is  Tery  pure.  Construction  of  a  still. 

glass  receiver  contained   in  a  vessel  filled  with  cold 
watery  and  is  then  condensed. 


Fig.  43. 

1298  Why  is  water  obtained  in  this  manner  by  distillation  purer  than 
spring  water  f 

Because  the  non-volatile,  earthy,  and  saline  portions 
contained  in  all  spring  waters  do  not  ascend  with  the 
vapor,  but  remain  in  the  retort.  By  this  means  very 
volatile  bodies  can  be  easily  separated  from  less  volatile 
ones ;  as  brandy  and  alcohol  from  the  less  volatile 
water  which  may  be  mixed  with  them. 

1J390  When  the  vessel  used  for  generating  the  vapor  is  very  large,  what 
is  it  called  f 

A  "still ;"  and,  for  con- 
densing the  vapor,  vats  are 
constructed,  holding  ser- 
pentine pipes  or  "  worms" 
which  present  a  greater 
condensing  surface  than 
if  the  pipe  had  passed  di- 
rectly through  the  vat. 

To  keep  the  coil  of  pipe  cool,  the 

vats  are  kept  filled  with  cold  water. 

Fig™  (See  Fig.  44.) 

In  this  figure  a  is  a  furnace,  in 

which  is  fixed  a  copper  vessel  to  contain  the  fluid.  Heat  being  applied, 
the  steam  rises  in  the  head  6,  and  passes  through  the  worm  d,  which  is 
placed  in  a  vessel  of  water,  the  refrigerator.  The  vapor  thus  generated  is 
condensed  in  its  passage,  and  passes  out  as  a  liquid  by  the  external  pipe 
into  a  receiver. 

13OO   What  is  the  difference  between  drying  by  heat  and  distil'tmg  f 


SCIENCE   OP   COMMON   THINGS.  197 

What  is  evaporation  ?  Danger  of  wearing  wet  clothes. 

In  the  one  case,  the  substance  vaporized,  being  of  no 
use,  is  allowed  to  escape  or  become  dissipated  in  the 
atmosphere ;  while  in  the  other,  being  the  valuable 
part,  it  is  caught  and  condensed  into  the  liquid  form. 

13O1   What  is  the  vapor  from  damp  linen  ? 

The  vapor  from  damp  linen,  if  caught,  would  be  dis- 
tilled water. 

13OS    What  is  evaporation  1 

The  conversion  of  a  fluid  into  vapor. 

"When  vaporization  takes  place  only  from  the  surface  of  a  body,  either 
because  the  heat  has  access  to  that  part,  or  because  the  evolution  of 
vapor  takes  place  through  the  medium  of  a  gas  or  air  already  present,  the 
action  can  only  be  recognised  by  the  diminution  of  the  bulk  of  the  body  : 
this  phenomenon  is  called  evaporation. 

1303  What  effects  are  produced  by  evaporation  f 

The  substance  vaporized  absorbs  heat  from  the  body 
whence  it  issues ;  and  the  body,  deprived  of  a  portion 
of  its  substance  by  evaporation,  loses  heat. 

1304  If  you  wet  your  finger  in  your  mouth,  and  hold  it  up  in  the  air, 
why  does  it  feel  cold  ? 

Because  the  saliva  quickly  evaporates,  and  (as  it 
evaporates)  absorbs  heat  from  the  finger,  making  it  feel 
cold. 

1305  If  you  lathe  your  temples  ivith  ether,  cologne  water,  spirits,  etc., 
why  does  it  allay  inflammation  and  feverish  heat? 

Because  these  liquids  very  rapidly  evaporate,  and  (as 
they  evaporate)  absorb  heat  from  the  burning  head, 
producing  a  sensation  of  cold. 

1306  Why  do  we  feel  cold  when  we  have  wet  feet  or  clothes  f 

Because  the  wet  of  our  shoes  or  clothes  rapidly  eva- 
porates, and  (as  it  evaporates)  absorbs  -heat  from  our 
body,  which  makes  us  feel  cold. 

ISO?    Why  do  wet  feet  or  clothes  give  us  "  cold?" 

Because  the  evaporation  absorbs  heat  so  abundantly 
from  the  surface  of  our  body,  that  its  temperature  is 
lowered  below  its  natural  standard  ;  in  consequence  of 
which  health  is  injured. 

13O8   Why  is  it  dangerous  to  skep  in  a  damp  bed? 

Because  the  heat  is  continually  absorbed  from  the 
9* 


198  SCIENCE   OF   COMMON   THINGS. 

Health  injured  by  reducing  the  temperature  of  the  body. 

surface  of  our  body  to  convert  the  damp  of  the  sheets 
into  vapor  ;  in  consequence  of  which  our  animal  heat 
is  reduced  'below  the  healthy  standard. 

1309  Why  is  health  injured  when  the  temperature  of  the  body  is 
reduced  below  its  natural  standard  f 

Because  the  balance  of  the  circulation  is  destroyed. 
Blood  is  driven  away  from  the  external  surface  by  the 
chill,  and  thrown  upon  the  internal  organs,  which  are 
oppressed  by  this  increase  of  Hood. 

1310  Why  do  we  not  feel  the  same  sensation  of  cold  if  we  throw  a 
waterproof  coat  over  our  wet  clothes  f 

Because  water-proof  coats  (being  air-tight)  prevent 
evaporation,  and  (as  the  wet  cannot  evaporate)  no  heat 
is  absorbed  from  our  bodies. 

1311  Why  does  sprinkling  a  hot  room  with  water  cool  it  f 

Because  the  heat  of  the  room  causes  a  rapid  evapora- 
tion of  the  sprinkled  water,  and  as  the  water  evaporates, 
it  absorbs  heat  from  the  room,  which  cools  it. 

131J3   Why  does  watering  the  streets  and  roads  cool  them  f 

Because  they  part  with  their  heat  to  promote  the  eva- 
poration of  the  water  spi^inkled  on  them. 

1313  Why  does  a  shower  of  rain  cool  the  air  in  summer-time  ? 

Because  the  wet  earth  parts  with  its  heat  to  promote 
evaporation  y  and  when  the  earth  is  cooled,  it  cools  the 
air  also. 

1314  Why  is  linen  dried  by  being  exposed  to  the  wind  f 

Because  the  wind  accelerates  evaporation  by  removing 
the  vapor  from  the  surface  of  the  wet  linen  as  fast  as  it 
is  formed. 

1315  Why  does  draining  land  promote  warmth, 

Because  abstracting  water  diminishes  evaporation  ; 
in  consequence  of  which  less  heat  is  withdrawn  from  the 
earth. 

1310   Why  does  cultivation  increase'the  warmth  of  a  country  f 

A  cultivated  country  is  better  drained,  and  laid  open 
to  the  rays  of  the  sun.  The  forests  being  cut  down, 
the  snow  quickly  disappears  in  the  spring,  and  the 
earth  soon  becomes  dry. 


SCIENCE   OF   COMMON   THINGS.  199 

Air  cool  after  a  rain.  Production  and  nature  of  steam. 

131V  Why  does  bread  after  the  lapse  of  a  few  days  become  dry  and 
stale  f 

Because  the  moisture  contained  in  it  evaporates  ;  the 
particles  then  shrink,  and  the  whole  mass  becomes 
hard. 

1318   Why  is  not  the  vapor  of  the  sea  salt  f 

Because  the  salt  is  always  left  behind  in  the  process 
of  evaporation. 

131O  "  AH  the  rivers  run  into  the  sea :"  why  is  not  the  sea  full  f 

Because  the  quantity  of  water  evaporated  from  the 
surface  of  the  sea  is  equal  to  the  quantity  poured  into 
it  by  the  rivers ;  therefore  the  sea  is  never  full. 

13J3O   Why  is  it  frequently  cooler  after  a  rain  f 

Because  water  which  falls  from  the  atmosphere  soon 
returns  to  it  in  the  form  of  vapor,  carrying  with  it,  in 
the  latent  form,  a  large  amount  of  heat  taken  from 
every  object,  thus  moderating  the  temperature  of  the 
earth,  and  refreshing  the  animal  and  vegetable  creations. 

1331  Does  evaporation  take  place  from  the  surface  of  snow  and  ice  f 

Yes,  to  a  very  considerable  extent,  even  when  the 
temperature  of  the  air  is  below  the  freezing  point. 

13SS   What  is  steam? 

The  vapor  of  boiling  water. 

1323  Is  steam  visible  or  invisible  f 

Steam  is  invisible;  but  when  it  comes  in  contact 
with  the  air  (being  condensed  into  small  drops)  it  in- 
stantly becomes  visible. 

13S4  How  do  you  know  that  steam  is  invisible  f 

If  you  look  at  the  spout  of  a  boiling,  kettle,  you  will 
find  that  the  steam  (which  issues  from  the  spout)  is 
always  invisible  for  about  half  an  inch,  after  which  it 
becomes  visible. 

1325   Why  is  the  steam  invisible  for  half  an  inch  t 

Because  the  air  is  not  able  to  condense  it,  as  it  first 
issues  from  the  spout ;  but  when  it  spreads  and  comes 
in  contact  with  a  larger  volume  of  air,  the  invisible 
steam  is  readily  condensed  into  visible  drops* 


200  SCIENCE  OF    COMMON   THINGS. 

Vapor  of  water  always  exists  in  air.  White  appearance  of  steam. 

1336  Does  air  ever  exist  without  steam  or  vapor  of  water  ? 

Air  without  steam  (theoretically  called  dry  air)  is 
not  ~known  to  exist  in  nature,  and  is  probably  not  pro- 
ducible by  art. 

1337*  Is  the  visible  matter,  popularly  called  steam,  really  true  steam  ? 

By  no  means,  and  should  be  carefully  distinguished 
from  steam  proper,  or  the  aeriform  state  of  water.  The 
cloud  or  smoke-like  matter  alluded  to  is  really  not  an 
air  or  vapor  at  all,  but  a  dust-like  cloud  of  minute 
bodies  of  liquid  water,  wafted  by  a  current  either  of 
true  steam,  or,  more  frequently,  of  mere  moist  air. 

1338  Is  it  necessary  to  the  production  of  steam  that  water  should  be 
raised  to  the  boiling  temperature  f 

It  is  not  /  the  surface  of  any  watery  liquid,  about  20° 
warmer  than  any  superincumbent  air  (however  warm 
or  cold  that  may  be),  rapidly  gives  off  true  steam,  which 
is  invisible,  but  which  no  sooner  mixes  with  colder  air 
than  it  is  recondensed  into  water,  and  assumes  the 
forms  of  minute  globules. 

1339  What  causes  the  visible  white  appearance  of  condensed  steam  f 

The  myriads  of  minute  globules  of  water  into  which 
the  steam  is  condensed  are  separately  invisible  to  the 
naked  eye,  but  each,  nevertheless,  reflects  a  minute  ray 
of  white  light.  The  multitudes  of  these  reflecting 
points,  therefore,  make  the  space  through  which  they 
are  diffused  appear  like  a  cloudy  body,  more  or  less 
white,  according  to  their  abundance. 

1330  In  what  manner  is  the  production  of  steam  in  boiling  water  first 
manifested  ? 

,  When  steam  begins  to  be  produced,  as  in  the  process 
of  making  water  boil,  and  the  heat  overcomes  the 
atmospheric  pressure  on  the  surface,  small  bubbles  are 
formed,  adhering  slightly  to  the  sides  of  the  vessel. 

1331  In  what  parts  of  the  boiler  will  its  development  be  most  conspicu- 
ous? 

The  bubbles  are  formed  most  rapidly  at  those  points 
against  which  the  flame  is  most  strongly  directed. 

1333  How  much  lighter  is  steam  than  water  f 


SCIENCE   OF   COMMON   THINGS. 


Different  spaces  occupied  by  steam  and  water.  Pressure  of  steam. 

About  1700   times  ;    because  a   quantity  of  water 
yields  nearly  1700  measures 
of  steam  at  212°  F. 

Fig.  45  represents  the  comparative 
volume  of  water  and  of  steam. 

1333  How  much  steam  will  a  cubic 
inch  of  water  furnish  1 

A  cubic  inch  of  water  ex- 
pands into  about  a  cubic  foot 
of  steam  at  212°  F.,  under  the 
ordinary  atmospheric  pres- 
sure. 

1334  Upon  what  does  the  power  of  .. 
steam  depend  f 

On  the  tendency  which  water  possesses  to  expand 
into  vapor  when  heated  to  a  certain  temperature. 

1335  What  is  the  most  important  property  of  steam  ? 

Its  elasticity  or  pressure.  By  virtue  of  this  property, 
when  freed  from  the  limits  which  confine  it,  steam  will 
dilate  into  any  space  to  which  it  may  have  access. 

133S  Jf  a  quantity  of  pure  steam  be  confined  in  a  close  vessel,  in  what 
manner  will  its  pressure  be  exerted  ? 

It  will  exert  on  every  part  of  the  interior  of  the  vessel 
a  certain  pressure  directed  outwards,  and  having  a  ten- 
dency to  burst  the  vessel. 

1337*  How  great  a  pressure  does  steam,  formed  under  ordinary  cir- 
cumstances, have  to  overcome  before  it  can  rise  from  the  surface  of  the  water  ? 

That  of  one  atmosphere  —  -fifteen  pounds  on  eveiy 
square  inch,  or  one  ton  on  every  square  foot  —  a  force 
equivalent  to  the  strength  of  six  hundred  horses. 

1338  What  happens  when  the  temperature  of  'steam  generated  under 
ordinary  pressures  is  reduced  below  212°  f1.  f 

It  is  immediately  condensed  into  water. 

1339  As  steam  sustains  and  elevates  a  weight  occasioned  by  the  pressure 
of  the  atmosphere,  of  fifteen  pounds  per  square  inch,  what  takes  place  when 
a  column  of  steam  is  immediately  condensed  ? 

The  atmospheric  weight  will  immediately  fall  writh  a 
force  equal  to  that  with  which  it  was  raised. 

1340  How  can  steam  be  used  to  advantage  for  cooking  vegetables,  etc.  f 


202  SCIENCE   OF   COMMON   THINGS. 

"What  is  high-pressure  steam  ?  What  is  a  steam-engine  ? 

In  cookery,  if  steam  raised  from  boiling  water  be 
allowed  to  pass  through  meat  and  vegetables,  it  will  be 
condensed  upon  their  surfaces,  imparting  to  them  the 
latent  heat  which  it  contained  before  its  condensation, 
thus  cooking  them  as  effectually  as  if  they  were  im- 
mersed in  boiling  water. 

1341   What  do  we  mean  when  we  speak  of  high-pressure  steam  f 

High-pressure  steam  is  merely  steam  condensed,  not 
by  withdrawal  of  heat,  but  by  pressure,  just  as  high- 
pressure  air  is  merely  condensed  air.  To  obtain  a 
double,  triple,  or  greater  pressure  of  steam,  we  must 
have  twice,  thrice,  or  more  steam  under  the  same  vo- 
lume. 

1343  Is  high-pressure  steam,  escaping  from  a  boikr  heated  to  300°  or 
more,  hotter  than  low-pressure  steam  escaping  from  a  boiler  at  212°  ? 

No  ;  for  the  instant  that  high-pressure  or  condensed 
steam  escapes  into  the  air,  it  immediately  expands  and 
becomes  low-pressure  steam,  and  is  greatly  cooled  down 
by  its  expansion. 

1343  Does  high-pressure  steam,  acting  in  a  boiler  at  a  high  tempera- 
ture,  exert  a  greater  mechanical  and  chemical  power  than  low-pressure 
steam  f 

It  does  f  high-pressure  steam  acting  upon  bones, 
breaks  up  and  dissolves  the  whole  mass,  extracting  all 
the  glue  and  fat,  when  ordinary  steam  would  dissolve 
nothing. 

In  the  Western  States,  where  large  quantities  of  lard  are  manufactured, 
the  whole  hog  is  exposed  to  high-pressure  steam,  and  the  carcass  reduced 
in  a  short  tune  to  a  fat  fluid  mass. 

1344  Can  high-pressure  steam  be  raised  to  a  very  elevated  degree  of 
heat? 

It  can  /  in  some  of  the  methods  lately  introduced  for 
purifying  oils,  etc.,  the  temperature  of  the  steam,  before 
its  application,  is  required  to  be  sufficiently  elevated  to 
enable  it  to  melt  lead. 

1345  What  is  the  steam-engine  f 

The  steam-engine  is  a  mechanical  contrivance  by 
which  coal,  wood,  or  other  fuel  is  rendered  capable  of 
executing  any  kind  of  labor. 


SCIENCE   OF  COMMON  THINGS.  203 

Mechanical  force  of  steam.         Comparison  of  steam  power  and  animal  power. 

1346  What  substance  furnishes  the  means  of  calling  the  powers  of  coal 
into  activity  ? 

Water. 

1347*  How  much  water  will  two  ounces  of  coal  evaporate  t 

About  a  pint. 

1348  How  much  steam  will  this  produce  f 

Two  hundred  and  sixteen  gallons. 

1340  How  much  mechanical  force  can  this  steam  exert  t 

It  can  raise  a  weight  of  thirty-seven  tons  to  the 
height  of  one  foot. 

1350  What  amount  of  force  can  a  man  exert  when  applying  his 
strength  to  the  best  advantage  through  the  help  of  machinery  f 

It  has  been  found  by  experiment,  that  a  man  work- 
ing on  a  tread-mill  continuously  for  eight  hours,  will 
elevate  one  and  a  half  millions  of  pounds  to  the  height 
of  one  foot. 

1351  With  how  much  coal  will  a  well  constructed  steam-engine  perform 
the  same  labor  ? 

With  the  expenditure  of  a  pound  and  a  half. 

1352  How  much  coal  then  would  be  equivalent  to  the  average  power  of 
an  able-bodied  man  during  his  active  life,  supposing  him  to  work  for  twenty 
years  at  Hie  rate  of  eight  hours  per  day  ? 

The  consumption  of  about  four  tons  of  coal  would 
evolve  in  a  steam-engine  fully  as  much  power. 

1353  The  great  pyramid  of  Egypt  is  five  hundred  feet  high,  and  weighs 
twelve  thousand  seven  hundred  and  sixty  millions  of  pounds.    Herodotus 
states  that  in  constructing  it  one  hundred  thousand  men  were  constantly 
employed  for  twenty  years.     With  how  much  coal  could  all  the  materials  of 
this  pyramid  be  raised  to  their  present  position  from  the  ground  ? 

With  the  expenditure  of  four  hundred  and  eighty 
tons  of  coal. 


204:  SCIENCE    OF   COMMON    THINGS. 

What  Is  ventilation  ?  Warming  and  ventilation  of  buildings. 


PART  VI. 

.VENTILATION  AND  WARMING,   COMBUSTION, 
RESPIRATION,  AND  NUTRITION. 


CHAPTEK   I. 

WARMING    AND    VENTILATION. 

1354  What  is  ventilation  f 

Ventilation  is  the  act  or  operation  of  causing  air  to 
pass  through  any  place,  for  the  purpose  of  expelling 
impure  air  and  dissipating  noxious  vapors. 

1355  What  is  the  theoretical  perfection  of  ventilation  ? 

To  render  it  impossible  for  any  portion  of  air  to  be 
breathed  twice  in  the  same  building. 

1356  Upon  what  principle  does  the  whole  process  of  warming  and  ven- 
tilating buildings  depend  ? 

Upon  the  expansion  and  contraction  of  air,  or,  in 
other  words,  upon  the  fact  that  air  which  has  been 
heated  and  expanded  ascends,  and  air  wrhich  has  been 
deprived  of  heat,  or  has  become  contracted,  descends. 

1357f  Is  there  an  upward  current  of  air  always 
rising  from  heated  substances  f 

There  is ;  air  made  lighter  by  heat 
ascends  through  colder  strata,  as  a  cork 
(put  at  the  bottom  of  a  basin  of  water) 
rises  to  the  surface. 

135S  What  simple  experiment  shows  the  exist* 
ence  of  this  upward  current  in  an  ordinary  stove  f 

If  we  attach  to  the  side  of  a  heated 
stovepipe  a  wire  on  which  a  piece  of 
paper  cut  in  the  form  of  a  spiral  may 


SCIENCE   OF   COMMON   THINGS.  205 

Why  a  fire  balloon  rises.  Where  ventilation  is  perfect.  Oxygen. 

be  suspended,  as  is  represented  in  Fig.  46,  the  upward 
current  of  hot  air  will  immediately  put  the  paper  in 
motion,  and  make  it  revolve  rapidly  around  the  wire. 

1359  When  a  boy  makes  a  fire-battoon,  and  sets  fire  to  the  cotton  or 
sponge  (which  has  been  steeped  in  spirits  of  wine),  why  is  the  balloon  inflated  f 

Because  the  air  of  the  balloon  is  expanded  by  the 
heat  of  the  flame,  and  fills  the  balloon  to  its  utmost 
capacity. 

1360  Why  does  the  balloon  rise  after  it  has  been  inflated  by  the  expanded 
air? 

Because  the  same  quantity  of  air  is  expanded  to  three 
or  four  times  its  orig^nal  volume  ;  and  made  so  much 
lighter,  that  even  when  all  the  paper,  wire,  and  cotton 
are  added,  it  is  still  lighter  than  common  air. 

1361  In  what  situation  is  ventilation  perfect  ? 

In  the  open  air,  because  the  breath,  as  it  leaves  the 
body,  is  warmer  and  lighter  than  the  surrounding  fresh 
air,  and  ascending  is  immediately  replaced  by  an  in- 
gress of  fresh  air  ready  to  be  received  by  the  next 
respiration. 

1363   Why  is  it  desirable  to  avoid  breathing  the  same  air  twice  ? 

Air  which  has  been  once  respired,  is  unwholesome, 
and  not  suited  to  supply  the  wants  of  the  animal  system. 

1363  What  are  the  elements  of  atmospheric  air? 

Oxygen  and  nitrogen  mixed  together,  in  the  propor- 
tion of  seventy-nine  parts  of  nitrogen  and  twenty-one 
of  oxygen. 

1364  What  is  oxygen  f 

A  gas,  colorless,  tasteless,  and  odorless ;  it  is  heavier 
than  atmospheric  air,  and  is  a  non-conductor  of  elec- 
tricity. 

1365  Is  oxygen  a  substance  existing  in  great  abundance  ? 

Oxygen  is  the  most  abundant  of  all  known  substances ; 
it  constitutes  at  least  one  third  of  the  solid  mass  of  the 
globe,  eight-ninths  of  all  water,  and  nearly  one-fourth 
part  of  the  atmosphere ;  it  also  exists  in  most  organic 
substances. 

1366  Is  oxygen  ever  found  in  a  liquid  or  solid  state  f 


206  SCIENCE  OF   COMMON  THINGS. 

Use  of  oxygen  in  the  air.  Nitrogen,  its  properties  and  us«s. 

~No ;  when  pure  it  is  only  known  in  the  gaseous  state ; 
all  efforts  to  reduce  it  to  a  liquid  or  solid  condition  by 
cold  or  pressure  have  completely  failed. 

1367  Of  what  use  is  oxygen  in  the  atmosphere  ? 

It  sustains  animal  life  and  supports  combustion. 

1368  If  an  animal  were  immersed  in  oxygen  gas,  would  it  continue  to 
live  for  a  time? 

It  would ;  at  the  same  time  animal  life  could  not  be 
sustained  for  any  great  length  of  time  in  an  atmosphere 
of  pure  oxygen. 

1369  What  is  meant  when  it  is  said  that  oxygen  "  sustains  life  f  " 

It  means  this :  if  a  person  could  not  inhale  oxygen, 
he  would  die. 

1370  What  good  does  this  inspiration  of  oxygen  do  f 

1.  It  gives  vitality  to  the  blood ;  and 

2.  It  is  the  cause  of  animal  heat. 

1371  What  is  nitrogen  f 

An  invisible  gas  existing  largely  in  atmospheric  air, 
and  in  most  animal  and  vegetable  substances. 

1372  What  are  its  principal  characteristics  f 

1.  It  is  not  combustible  / 

2.  It  does  not  support  animal  life  ;  and 

3.  It  is  the  principal  ingredient  in  the  composition 
of  atmospheric  air. 

1373  What  proportion  of  the  air  we  breathe  is  composed  of  nitrogen  f 

About  four  -fifths  of  the  air  is  nitrogen  /  the  other 
one-fifth  is  oxygen. 

1374  Why  is  there  so  much  nitrogen  in  the  air  f 

The  uses  of  nitrogen  are  in  a  great  measure  unknown. 
It  has  been  supposed  to  act  as  a  diluent  to  the  oxygen, 
but  it  most  probably  serves  some  useful  purpose  in  the 
economy  of  animals  and  vegetables,  the  exact  nature  of 
which  has  not  been  discovered. 

1375  What  would  be  the  effect  if  the  proportion  of  oxygen  in  the  atmo- 
sphere were  increased  f 

The  inflammability  of  most  substances  would  be  in- 
creased, fires  would  burn  out  very  quickly,  and  the 


SCIENCE  OF  COMMON   THINGS.  207 

Carbonic  acM  gas.  The  composition  of  the  air  never  varies. 

functions  of  life  would  be  called  into  such  rapid  action 
as  to  soon  exhaust  the  powers  of  the  system. 

1370  Are  the  two  gases,  oxygen  and  nitrogen,  existing  in  tlie  atmo- 
sphere, chemically  combined,  or  merely  intermingled  ? 

They  are  merely  mixed,  and  not  combined  with  each 
other. 

1377'  Does  thv  atmosphere  always  contain  any  other  ingredients  besides 
oxygen  and  nitrogen  f 

There  is  always  in  the  air,  at  all  places,  carbonic  acid 
gas,  in  variable  proportions,  and  watery  vapor,  besides 
the  odoriferous  matter  of  flowers  and  other  volatile 
substances. 

1378  What  is  carbonic  acid  gas  f 

A  gas  formed  by  the  union  of  carbon  and  oxygen ; 
it  used  to  be  called  fixed  air.  Its  chemical  com- 
position is  one  atom  of  carbon  united  to  two  of 
oxygen. 

1379  Is  the  air  collected  on  the  tops  of  high  mountains,  over  marshes 
in  hospitals,  and  over  deserts,  the  same  in  character  and  composition  f 

It  is  not  found  to  vary,  but  is  the  same  in  all  regions 
of  the  earth  and  at  all  altitudes. 

1380  Are  the  component  parts  of  air,  oxygen,  nitrogen,  carbonic  acid, 
and  watery  vapors,  of  different  specific  gravities,  or  do  they  all  differ  in 
weight  ? 

They  are  all  different,  carbonic  acid  gas  being  the 
heaviest. 

1381  Then,  as  we  have  before  stated  that  they  are  merely  mixed,  and 
not  combined,  why  do  they  not  arrange  themselves  in  the  order  of  their  densi- 
ties, and  float  one  upon  the  other,  as  oil  and  water  do  when  mingled  f 

Because  of  a  wonderful  principle  or  law  of  nature, 
that  when  two  gases  of  different  weights  or  specific 
gravities  are  mixed  together,  they  cannot  remain  sepa- 
rate, as  fluids  of  different  densities  do,  but  diffuse  them- 
selves uniformly  throughout  the  whole  space  which 
both  occupy. 

1383  Carbonic  acid  is  tiventy  times  heavier  than  hydrogen  gas ;  if  we 
fill  the  lower  part  of  a  tatt  jar  with  carbonic  acid,  and  the  upper  part  with 
kydrogen,  will  the  two  gases  mix  ? 

After  a  few  hours  the  two  gases  will  be  found  equally 


208  SCIENCE    OF    COMMON   THINGS. 

Carbonic  acid  gas  in  the  atmosphere. 

mingled,  as  much  carbonic  acid  being  at  the  top  of  the 
jar  as  at  the  bottom. 

13 S3  Does  this  law  appear  to  be  opposed  to  the  principles  of  the  law  of 
gravitation  ? 

It  appears  to  be  opposed  to  it ;  the  only  exception  we 
are  acquainted  with  in  the  natural  world. 

1384  How  much  carbonic  acid  is  estimated  to  exist  in  the  atmosphere  f 

I     About  one  part  in  two  thousand,  by  volume. 

1335  If  this  were  all  collected  in  one  layer  over  the  surface  of  the  earth, 
how  great  a  thickness  would  this  layer  or  stratum  have  ? 

About  thirteen  feet. 

138Q    Can  we  breathe  carbonic  acid? 

No  •  the  animal  immersed  in  it  dies  instantly. 

1387*  If,  then,  this  singular  law  of  the  diffusion  of  gases  did  not  prevail, 
would  the  surface  of  the  earth  be  habitable  ? 

It  would  not;  carbonic  gas  would  fill  up  all  the 
valleys  and  lower  levels,  separating  every  hill  and  ele- 
vation •  by  an  invisible  ocean  of  poisonous  gas,  as  im- 
passable as  the  barrier  between  the  dead  and  the 
living. 

1388  Is  it  owing  to  this  law  that  we  are  enabled  to  enjoy  and  perceive 
at  a  distance  the  odor  of  a  flower-garden,  or  the  perfume  which  has  been 
opened  in  an  apartment  f 

It  is  by  this  law  that  a  vapor,  arising  by  its  own 
elasticity  from  a  volatile  substance,  is  caused  to  extend 
its  influence  and  mingle  with  the  surrounding  atmo- 
sphere, until  its  effects  become  so  enfeebled  by  dilution 
as  to  be  imperceptible  to  the  senses. 

138Q  If  the  oxygen  and  nitrogen  of  which  our  atmosphere  is  composed 
were  combined  together,  instead  of  being  merely  mingled,  what  would  the 
compound  be  ? 

A  most  deadly  poison. 

1390  What  gas  is  generated  by  a  lighted  candle  or  lamp  ? 

Carbonic  acid  gas — formed  by  the  union  of  the  carbon 
of  the  oil  or  tallow  with  the  oxygen  of  the  air. 

1391  Under  what  circumstances  does  carbon  most  readily  unite  with 
oxygen  ? 

1.  When  its  temperature  is  raised :  thus,  if  carbon 
be  red  hot,  oxygen  will  most  readily  unite  with  it ; 


SCIENCE   OF   COMMON   THINGS.  209 

Carbonic  acid  a  poison.  Crowded  room  unhealthy. 

2.  Carbon  in.  the  Hood  unites  readily  -with  oxygen 
during  respiration  ;  and 

3.  Carbonic  acid  is  formed  in  large  quantities  during 
the  chemical  changes  which  we  call  fermentation. 

1302  Js  carbonic  acid  in  any  degree  wholesome  f 

No  /  it  is  fatal  to  animal  life,  and  (whenever  it  is 
inhaled)  acts  like  a  narcotic*  poison,  producing  drowsi- 
ness, which  sometimes  ends  in  death. 

1303  When  persons  commit  suicide  by  building  a  charcoal  fire  in  a 
closed  room,  what  occasions  their  death  ? 

The  inhalation  of  carbonic  acid,  which  is  generated 
by  the  combustion  of  the  charcoal. 

1304  How  can  any  one  know  if  a  place  be  infested  with  carbonic  acid 
gasf 

If  a  pit  or  well  contain  carbonic  acid,  a  lighted  candle 
(let  down  into  it)  will  be  instantly  extinguished.  The 
rule,  therefore,  is  this :  where  a  candle  will  burn,  a  man 
can  live  /  but  what  will  extinguish  a  candle,  will  also 
destroy  life. 

1305  Why  does  a  crowded  room  produce  headache? 

Because  we  breathe  air  vitiated  by  the  crowd. 

1306  Why  is  the  air  of  a  room  vitiated  by  a  crowd  ? 

Because  it  is  deprived  of  its  due  proportion  of  oxy- 
gen, and  loaded  with  carbonic  acid. 

1307*  How  is  the  air  of  a  room  affected  thus  by  a  crowd  ? 

The  elements  of  the  air  inhaled  are  separated  in  the 
lungs  ;  the  oxygen,  incorporated  in  the  blood,  forms 
carbonic  acid  ;  and  the  carbonic  acid  (together  with 
the  nitrogen)  is  thrown  back  again  by  the  breath  into 
the  room, 

1308  Is  all  the  nitrogen  rejected  by  the  lungs  f 

Yes ;  all  the  nitrogen  of  the  air  is  always  expired. 

1300  How  much  oxygen  does  afull-groivn  person  consume  per  hourf 

It  is  calculated  that  an  adult  of  average  size  absorbs 

*  A  narcotic  is  a  substance  which,  when  used  as  a  medicine,  relieves 
pain  and  produces  sleep,  but  in  poisonous  doses  produces  death.  Opium, 
laudanum,  tobacco,  etc,,  are  narcotics. 


210  SCIENCE   OF   COMMON   THINGS 

Air  consumed  by  a  person  in  an  heur.  Vegetation  purifies  the  air. 


about  a  cubic  foot  of  oxygen  per  hour  by  respiration, 
and  consequently  renders  five  cubic  feet  of  air  unfit  for 
breathing,  since  every  five  cubic  feet  of  air  contain  one 
cubic  foot  of  oxygen.  It  is  also  calculated  that  two 
wax  or  sperm  candles  absorb  as  much  oxygen  as  an 
adult. 

1400  To  keep  tJie  air  of  a  room  pure,  how  much  fresh  air  should  be 
allowed  to  pass  in  per  hour  f 

Five  cubic  feet  for  each  person,  and  two  and  a  half 
cubic  feet  for  each  candle,  should  be  allowed  to  pass  in, 
and  an  equal  quantity  to  pass  out. 

1401  Why  do  persons  in  a  crowded  church  feel  drowsy  f 

1.  Because  the  crowded  congregation  inhale  a  large 
portion  of  the  oxygen  of  the  air,  which  alone  can  sus- 
tain vitality  and  healthy  action  ;  and 

2.  The  air  of  the  church  is  impregnated  with  carbonic 
acid  gas,  which   (being  a  strong   narcotic)   produces 
drowsiness  in  those  who  inhale  it. 

14OS  Why  do  persons  who  are  much  in  the  open  air  enjoy  the  best 
health  f 

Because  the  air  they  inhale  is  much  more  pure  than 
the  air  of  close  and  confined  rooms. 

1403  How  does  vegetation  (trees  and  flowers]  serve  to  purify  the  airf 

1.  Because  trees  and  flowers   absorb   the   carbonic 
acid  generated  by  the  lungs  of  animals,  putrid  sub- 
stances, and  other  obnoxious  exhalations ;  and 

2.  Trees  and  flowers  restore  to  the  air  the  oxygen 
which  man  and  other  animals  inhale. 

1404  Why  is  the  air  of  cities  generally  less  pure  than  the  air  of  the 
open  country  f 

1.  Because  there  are  more  inhabitants  to  vitiate  the 
air; 

2.  The  sewers,  drains,  bins,  and  filth  of  a  city  very 
greatly  vitiate  the  air  ; 

3.  The  streets  and  alleys  prevent  a  free  circulation ; 
and 

4.  There  are  fewer  trees  to  absorb  the  excess  of  car- 
bonic acid  gas,  and  restore  the  equilibrium. 


SCIENCE   OF   COMMON   THINGS.  211 

* ,. • 

Close  rooms  unhealthy.  Carbon  thrown  off  by  the  lungs. 

1405  Why   are  persons  who  live  in  close  rooms  and  crowded'  cities 
generally  sickly  f 

Because  the  air  they  breathe  is  not  pure,  but  is  (in 
the  first  place)  defective  in  oxygen,  and  (in  the  second) 
is  impregnated  with  carbonic  acid  gas. 

1406  Where  does  the  carbonic  acid  of  close  rooms  and  cities  com* 
from  ? 

From  the  lungs  of  the  inhabitants,  the  sewers,  drains, 
and  other  like  places,  in  which  organic  substances  are 
undergoing  decomposition. 

1407  What  becomes  of  the  carbonic  acid  generated  in  crowded  cities  f 

It  is  gradually  diffused  through  the  air,  absorbed  by 
vegetation  and  by  water,  and  wafted  by  the  winds  to 
different  localities. 

1408  Does  not  this  constant  diffusion  of  carbonic  acid  affect  the  purity 
of  the  whole  air  1 

No  ;  because  it  is  wafted  by  the  wind  from  place  to 
place,  and  absorbed  in  its  passage  by  the  vegetable  world. 

1409  What  is  choke  damp  ? 

Carbonic  acid  gas  accumulated  at  the  bottom  of  wells 
and  pits,  which  renders  them  noxious,  and  often  fatal  to 
life.  It  is  called  choke  damp,  because  it  chokes  (or  suf- 
focates) every  animal  that  attempts  to  inhale  it. 

It  suffocates  without  getting  into  the  lungs,  by  closing  the  glottis  spas' 
modicatty. 

1410  Why  is  not  this  carbonic  acid  taken  up  by  the  air  and  diffused,  as 
it  is  in  tities  f 

Because  (being  heavier  than  common  air)  it  cannot 
readily  rise  from  the  well  or  pit ;  and  no  wind  can  get 
to  it  to  blow  it  away. 

By  the  chemical  law  of  diffusion,  a  portion  of  the  carbonic  acid  which 
accumulates  at  the  bottom  of  wells  and  pits,  is  removed ;  but  in  many 
cases  this  abstraction  is  more  than  counterbalanced  by  an  increased 
supply. 

1411  How  much  carbon  in  the  form  of  carbonic  acid  passes  through  the 
lungs  of  a  healthy  person  every  twenty-four  hours  f 

The  quantity  would  be  very  accurately  represented 
by  a  mass  of  charcoal  of  the  weight  of  fifteen  ounces. 

The  volume  of  carbon  in  the  atmosphere,  although  it  forms  but  one  per 
cent,  of  the  carbonic  acid  existing  in  it,  exceeds  in  amount  all  the  carbon 


212  SCIENCE   OF   COMMON   THINGS. 

Sources  of  carbonic  acid.  The  air  always  in  motion. 


that  is  stored  in  the  earth  in  the  form  of  coal,  or  spread  over  its  surface  in 
the  form  of  animals  or  vegetables. 

141S    What  are  the  chief  sources  of  carbonic  acid  ? 

Combustion,  respiration  of  men  and  animals,  the 
decomposition  of  organic  substances,  and  the  exhalations 
of  volcanoes.  Carbonic  acid  also  exists  in  large  quan- 
tities in  the  atmosphere,  in  most  waters,  and  combined 
with  minerals  in  a  solid  state,  as  in  marble,  which  con- 
sists of  lime  united  to  carbonic  acid. 

1413  From  which  of  these  sources  is  carbonic  acid  most  likely  to  accu- 
mulate to  a  noxious  extent  f 

From  the  fermentation  arid  putrefaction  of  decaying 
vegetable  and  animal  matters. 

1414  How  can  this  accumulation  of  carbonic  acid  be  prevented? 

By  throwing  quicklime  into  places  where  such  fer- 
mentation ana  putrefaction  are  going  on. 

1415  How  will  quicklime  prevent  the  accumulation  of  carbonic  acid? 

Quicklime  will  absorb  the  carbonic  acid,  and  produce 
a  combination  called  "  carbonate  of  lime." 

1416  Does  not  heavy  rain,  as  well  as  quicklime,  prevent  the  accumula- 
tion of  carbonic  acidf 

Yes  ;  an  abundant  supply  of  water  will  prevent  the 
accumulation  of  carbonic  acid,  by  dissolving  it. 

1417  Is  the  external  air  always  in  motion? 

Some  portion  of  the  atmosphere  is  always  in  motion. 
Currents  of  warm  air  ascending,  and  currents  of  cold 
air  descending. 

1418  7s  the  air  of  our  rooms  always  in  motion  f 

Yes ;  there  are  always  two  currents  of  air  in  the 
room  we  occupy ;  one  of  hot  air  flowing  out  of  the 
room,  and  another  of  cold  air  flowing  into  the  room. 

1419  How  do  you  know  that  there  are  these  two  currents  of  air  in 
wery  occupied  room  f 

If  I  hold  a  lighted  candle  near  the  crevice  at  the  top 
of  the  door,  the  flame  will  be  blown  outwards  (towards 
me  hall) ;  but  if  I  hold  the  candle  at  the  bottom  of 
the  door,  the  flame  will  be  blown  inwards  (into  the 
room). 


SCIENCE  OF   COMMON   THINGS.  213 

Causo  of  air  currents  at  windows  and  doors.  What  is  a  vacuum  ? 

This  is  not  the  case  if  a  fire  be  in  the  room.  When  a  fire  is  lighted, 
an  inward  current  is  drawn  through  all  the  crevices. 

1430  Why  would  the  flame  'be  blown  outvjards  (towards  the  hall)  if  a 
candle  be  held  at  the  top  of  the  door  ? 

Because  the  air  of  the  room  being  heated,  and  con- 
sequently ratified,  ascends,  and  (floating  about  the 
upper  part  of  the  room)  some  of  it  escapes  through  the 
crevice  at  the  top  of  the  door,  producing  a  current  of 
air  outwards  (into  the  hall). 

1431  Why  would  the  flame  be  blown  inwards  (into  the  room)  if  the 
candle  be  held  at  the  bottom  of  the  door  ? 

Because  a  partial  vacuum  is  made  at  the  bottom  of 
the  room,  as  soon  as  the  warm  air  of  the  room  has 
ascended  to  the  ceiling  or  made  its  escape  from  the 
room ;  and  the  cold  air  from  the  hall  ruslies  under  the 
door  to  supply  the  void. 

1433  What  is  meant  by  a  partial  vacuum  being  made  at  the  bottom 
of  the  room  ? 

It  here  signifies  a  place  from  which  the  air  has  been 
taken  /  and  a  "  partial  vacuum"  means  a  place  from 
which  a  part  of  the  air  has  been  taken  away.  Thus, 
when  the  air  near  the  floor  ascends  to  the  ceiling,  a 
partial  vacuum  is  made  near  the  floor. 

1433  And  how  is  the  vacuum  filled  up  again  f 

It  is  filled  up  by  colder  air,  which  rushes  (under  the 
door,  and  through  the  window  crevices)  into  the  room. 

1434  Give  me  an  illustration. 

If  I  dip  a  pail  into  a  pond  and  fill  it  with  water,  a 
hole  (or  vacuum)  is  made  in  the  pond  as  big  as  the 
pail  ;  but  the  moment  I  draw  the  pail  out,  the  hole  is 
Jilled  up  by  the  water  around. 

1435  Show  how  this  illustration  applies. 

The  heated  air  which  ascends  from  the  bottom  of  a 
room  is  as  much  taken  away  as  the  water  in  the  pail, 
and  (as  the  void  was  instantly  supplied  by  other  water 
in  the  pond)  so  the  void  of  air  is  supplied  by  the  air 
around. 

1436  Why  is  a  room  (even  without  a  fire)  generally  warmer  than  ifa 

epsn  air? 

10 


214 


SCIENCE  OF  COMMON   THINGS. 


"Why  smoke  ascends  the  chimney. 


What  is  the  draught  of  a  chimney  ? 


Because  the  air  in  a  room  is  not  subject  to  much 
change,  and  soon  partakes  of  the  same  temperature  as 
our  bodies,  when  it  no  longer  feels  cold. 

1437*   Why  do  we  generally  feel  colder  out-of-doors  than  in-doorsf 

Because  the  air  (which  surrounds  us)  is  always 
changing  /  and  as  fast  as  one  portion  of  air  has  become 
warmer  by  contact  with  our  body,  another  colder  por- 
tion surrounds  us,  to  absorb  more  heat. 

1458  Why  is  there  always  a  draught  through  the  window  crevices  ? 

Because  the  external  air  (being  colder  than  the  air 
of  the  room  we  occupy)  rushes  through  the  window 
crevices,  to  supply  the  deficiency  caused  by  the  escape 
of  warm  air  up  the  chimney,  etc. 

1459  Why,  when  we  kindle  a  fire  in  a  stove  or  grate,  does  the  smoke 
ascend  the  chimney  ? 

When  a  fire  is  lighted  to  warm  a  room,  the  smoke 
and  other  gaseous  products  of  combustion,  being  lighter 
than  the  air  of  the  room,  ascend,  and  soon  fill  the  chim- 
ney with  a  column  of  air  lighter,  bulk  for  bulk,  than 
a  column  of  atmospheric  air. 

143O  /s  the  column  of  light  air  in  the  chimney  pressed  up  by  a  column 
of  equal  size  on  the  exterior  of  the  chimney  f 

It  is. 

1431  What,  then,  is  the  draught  of 
a  chimney  f 

It  is  the  rate  or  speed  with 
which  the  column  of  cold  air 
outside  the  chimney  pushes 
up  the  column  of  warm  air 
inside  the  chimney,  and  this 
draught  will  be  strong  and 
effective  just  in  the  same 
proportion  as  the  column  of 
air  in  the  chimney  is  kept 
warm. 


Fig.  47  represents  a  section  of  a 
grate  and  chimney.  C  D  represents 
the  light  and  warm  column  of  air  with- 
in the  chimney,  and  A  B  the  cold  and 
heavy  column  of  air  outside  the  chim- 


A! 


47 


SCIENCE   OF   COMMON   THINGS. 


215 


Use  of  chimneys. 


Utility  of  long  chimneys. 


ney.  The  column  A  B  being  cold  and  heavy  presses  down,  the  column  C 
t)  being  light  and  warm  rushes  up,  and  the  greater  the  difference  between 
the  weight  of  these  two  columns,  the  greater  will  be  the  draught. 

14353  IIow  do  chimneys  quicken  the  ascent  of  hot  air  ? 

By  keeping  a  long  column  of  it  together.  A  column 
of  two  feet  high  rises,  or  is  pressed  up,  with  twice  as 
much  force  as  a  column  of  one  foot,  and  so  in  propor- 
tion for  all  other  lengths — just  as  two  or  more  corks, 
strung  together  and  immersed  in  water,  tend  upwards 
with  proportionally  more  force  than  a  single  cork. 

In  a  chimney  where  one  foot  in  height  of  the  column  of  hot  air  is  one 
or.r.ce  lighter  than  the  same  bulk  of  external  cold  air,  if  the  chimney  be 
one  undred  feet  high,  the  air  or  smoke  in  it  is  propelled  upwards  with 
a  fore,  of  one  hundred  ounces. 

143.     To  what  is  the  draught  of  a  chimney  in  all  cases  proportioned  to  f 

With  sufficient  fire,  to  the  length  of  the  chimney. 

1434  Why  are  the  chimneys  of  large  manufactories  generally  very 
high  ? 

A  long  chimney  causes  a  current 
of  air  to  pass  through  a  fire  very 
rapidly,  and  at  the  same  time  very 
uniformly.  On  these  accounts,  for  the 
fires  of  steam-engines,  etc.,  long  chim- 
neys are  preferred. 

1435  When  the  temperature  of  the  air  in  a  room 
and  of  the  air  outside  are  the  same,  will  there  be  any 
draught  up  the  chimney  ? 

There  will  be  no  draught. 

143  6  When  there  is  no  fire  in  stove  or  grate,  and 
the  air  of  a  room  is  warmer  than  the  air  outside,  will 
there  be  a  circulation  up  and  down  the  chimney? 

In  such  cases  there  will  generally  bo 
two  currents,  up  and  down  the  chim- 
ney, especially  if  the  doors  and  win- 
dows of  the  room  be  tight.  The  warm 
air  of  the  room  will  ascend  through  the 
chimney,  and  the  cold  air  descend  by 
the  side  of  it,  two  currents  readily  cir- 
culating through  one  tube.  The  direc- 
tion of  the  arrows,  in  Fig.  48,  will  show  Fig.  48. 


216  SCIENCE   OF   COMMON    THINGS. 

How  to  construct  a  chimney.  Use  of  a  cowl  upon  a  chimney. 

the  lines  of  the  current,  descending  the  chimney  and 
circulating  round  the  apartment. 

143  7*  Why  does  an  apartment  often  smell  disagreeably  of  soot  in  sum- 
mer-time ? 

Because  the  air  in  the  chimney  (being  colder  than 
the  air  in  the  apartment)  descends  into  the  room,  and 
leaves  a  disagreeable  smell  of  soot  behind. 

1438  How  ought  chimneys  to  be  constructed? 

A  chimney  should  be  constructed  in  such  a  way 
that  the  flue  or  passage  will  gradually  contract  from  the 
bottom  to  the  top,  being  widest  at  the  bottom,  and  the 
smallest  at  the  top. 

1439  Why  is  it  expedient  to  construct  a  chimney  in  iliis  manner  f 

At  the  base  of  the  chimney,  the  hot  column  of  air  fills 
the  entire  passage ;  but  as  the  hot  air  ascends  it 
gradually  cools  and  contracts,  occupying  less  space.  If, 
therefore,  the  chimney  were  of  the  same  size  all  the 
way  up,  the  tendency  would  be,  that  the  cold  external 
air  would  rush  down  to  fill  up  the  space  left  by  the  con- 
traction of  the  hot  column  of  air.  This  action  would 
still  farther  cool  the  hot  air  of  the  chimney  and 
diminish  the  draught. 

14:40   Why  will  a  long  chimney  smoke,  unless  the  fire  be  pretty  fierce  f 

Because  the  heat  of  the  fire  will  not  be  sufncient  to 
rarefy  all  the  air  in  the  chimney. 

1441  Why  will  the  chimney  smoke,  unless  the  fire  be  fierce  enough  to 
heat  all  the  air  in  the  chimney-flue  f 

Because  the  cold  air  (condensed  in  the  upper  part  of 
the  flue)  will  sink  from  its  own  weight  ;  and  sweep 
the  ascending  smoke  back  into  the  room. 

144S   What  is  the  use  of  a  cowl  upon  a  chimney-pot  f 

It  acts  as  a  screen,  to  prevent  the  wind  from  blowing 
into  the  chimney. 

1443  What  harm  would  the  wind  do  if  it  were  to  blow  into  a  chim- 
ney? 

1.  It  would  prevent  the  smoke  from  getting  out ; 
and 

2.  The  cold  air  (introduced  into  the  chimney  by  the 


SCIENCE   OF   COMMON   THINGS.  217 

Use  of  a  blower  upon  a  grate.  Hottest  arid  coolest  portions  of  a  room. 

wind)  would  fall  down  the  fiue,  and  drive  the  smoke 
with  it  into  the  room. 

1444  Why  do  some  chimneys  smoJce  ? 

Because  fresh  air  is  not  admitted  into  a  room  as  fast 
as  it  is  consigned  by  the  fire  ;  in  consequence  of  which 
a  current  of  air  rushes  down  the  chimney  to  supply  the 
deficiency,  driving  the  smoke  along  with  it. 

1445  Why  do  Mowers,  when  placed  before  a  grate,  tend  to  kindle  the 
fire? 

A  blower  is  a  sheet  of  iron  that  stops  up  the  space 
above  the  grate  bars,  and  prevents  any  air  from  enter- 
ing the  chimney  except  that  which  passes  through  the 
fuel  and  produces  combustion.  This  soon  causes  the 
column  of  air  in  the  chimney  to  become  heated,  and  a 
draught  of  considerable  force  is  speedily  produced 
through  the  fire.  The  increase  of  draught  increases  the 
intensity  of  the  lire. 

1446  Which  is  the  hottest  part  of  a  room  ? 

The  upper  part,  near  the  ceiling.  The  warm  air 
being  the  lightest  seeks  the  highest  position. 

1447  Which  is  the  coolest  part  of  a  room  f 

The  lowest  part,  near  the  floor.  Cold  air  being  dense 
and  heavy  seeks  the  lowest  position. 

144S  By  which  means  is  a  room  better  ventilated,  by  opening  the  uppef 
or  the  lower  sash  ? 

A  room  is  better  ventilated  by  opening  the  upper 
sash  •  because  the  hot  vitiated  air  (which  always  as- 
cends towards  the  ceiling)  can  escape  more  easily. 

1449  What  temperature  is  most  proper  for  keeping  an  apartment  in 
a  healthy  and  pleasant  condition  during  the  cold  season  f 

From  65°  to  70°  F.,  with  a  free  ventilation. 

1450  How  are  houses  and  other  buildings  heated  with  hot  air  f 

The  fire  is  kindled  in  a  furnace  which  is  erected  in 
the  cellar.  This  fire  heats  the  air  in  contact  with  it  in 
the  air-chainber,  as  it  is  called,  and  as  heated  air 
always  ascends,  it  is  forced  up  into  the  different  apart- 
ments of  the  building. 


218  SCIENCE   OF   COMMON   THINGS. 

What  is  smoke  ?  Open  fireplaces  111  adapted  for  heating  rooms. 


1451  Which  would  prove  the  warmest  upon  a  bed — a  blanket,  or  an 
oiled  silk,  or  India-rubber  air-tight  covering  f 

The  air-tight  covering. 

1453  Why  do  we  not  use  oiled  silk  or  India-rubber  bed  coverings  in 
the  winter  ? 

Because  they  prevent  ventilation,  and,  by  shutting 
in  the  insensible  perspiration,  soon  produce  dampness. 

1453  What  is  smoke? 

Small  particles  of  carbon  separated  by  combustion 
from  the  fuel,  but  not  consumed. 

1454  Is  there  a  circulation  of  the  air  through  the  bed  coverings  at 
night? 

Yes  ;  from  every  part  of  the  bed-clothes  immediately 
over  the  person  there  is  a  constant  outward  oozing  of 
warm  air,  and  an  oozing  inwards  of  cold  air  in  lower 
situations  around. 

1455  In  what  two  ways  is  heat  communicated  to  apartments  by  fires 
kept  in  them  ? 

By  radiation  and  immediate  contact. 

The  first  portion  passes  through  the  air  in  diverging  lines  with  great 
velocity.  The  second  penetrates  slowly  through  the  substance  of  the 
densest  bodies.  To  enjoy  the  full  effect  of  radiated  heat,  we  mus,t  be  in 
the  presence  or  sight  of  the  radiating  object.  To  receive  conducted  heat, 
we  must  be  in  contact,  either  directly  or  through  some  intervening  me- 
dium, with  the  body  that  imparts  it. 

1456  Does  a  person  who  sits  by  afire  in  the  open  air  receive  any  heat 
by  conduction? 

Very  little;  for  the  air  which  surrounds  the  fire 
having  nothing  to  confine  it,  ascends  by  its  diminished 
specific  gravity  as  fast  as  it  is  warmed,  and  its  place  is 
immediately  supplied  by  strata  of  cold  air  from  beneath. 

1457  Will  a  person  sitting  beside  a  fire  in  the  open  air  be  exposed, 
ipon  the  side  of  his  body  removed  from  the  fire,  to  additional  cold? 

He  will,  because  cold  currents  rush  in  from  every 
nde  towards  the  fire. 

1458  Why  are  open  fireplaces  ill  adapted  for  the  economical  heating 
")f  apartments  ? 

In  an  open  fireplace  the  air  flows  from  the  room  to 
the  fire,  becomes  heated,  and  passes  off  directly  into 
the  chimney,  without  having  an  opportunity  of  parting 


SCIENCE  OF  COMMON  THINGS.  219 

Advantages  of  stoves  over  fireplaces.  Disadvantages  of  stoves. 

with  its  heat  for  any  useful  purpose.  In  addition  to 
this,  a  quantity  of  the  air  of  the  room,  which  has  been 
warmed  by  radiation,  is  uselessly  carried  away  by  the 
draught. 

1459  What  are  Vie  advantages  of  a  stove  over  an  open  fireplace  ? 

1.  Being  detached  from  the  walls  of  the  room,  the 
greater  part  of  the  heat  produced  by  combustion  is 
saved.     The  radiated  heat  being  thrown  into  the  walls 
of  the  stove,  they  become  hot,  and  in  turn  radiate  heat 
on  all  sides  to  the  room.     The  conducted  heat  is  also 
received  by  successive  portions  of  the  air  of  the  room, 
which  pass  in  contact  with  the  stove ; 

2.  The  air  being  made  to  pass  through  the  fuel,  a 
small  supply  is  sufficient  to  keep  up  the  combustion,  so 
that  little  need  be  taken  out  of  the  room  ;  and 

3.  The  smoke,  in  passing  off  by  a  pipe,  parts  with 
the  greater  part  of  its  heat  before  it  leaves  the  room. 

1460  What  are  the  disadvantages  of  stoves  ? 

Houses  containing  them  are  generally  ill  ventilated. 
The  air  coming  in  contact  with  the  hot  metal  surfaces 
is  rendered  impure,  which  impurity  is  increased  by  the 
burning  of  the  dust  and  other  substances  which  settle 
upon  the  stove.  The  air  is,  in  most  cases,  kept  so  dry 
as  to  render  it  oppressive. 

1461  Upon  what  principle  are  the  common  hot-air  furnaces  for  warm- 


A  stove,  having  large  radiating  surfaces,  is  inclosed 
in  a  chamber  (generally  of  masonry).  This  chamber 
is  generally  built  with  double  walls,  that  it  may  be  a 
better  non-conductor  of  heat.  A  current  of  air  from 
without  is  brought  by  a  pipe  or  box,  and  delivered  un- 
der the  stove.  A  part  of  this  air  is  admitted  to  supply 
the  combustion  ;  the  rest  passes  upwards  in  the  cavity 
between  the  hot  stove  and  the  walls  of  the  brick  cham- 
ber, and,  after  becoming  thoroughly  heated,  is  con- 
ducted through  passages  in  which  its  lightness  causes 
it  to  ascend,  and  be  delivered  in  any  apartment  of  the 
house. 


220  SCIENCE    OF   COMMON   THINGS. 

Construction  of  furnaces.  Combustion. 

1463  In  the  construction  and  arrangement  of  a  furnace  for  warming, 
what  two  points  are  of  special  importance,  so  far  as  regards  the  economy  of 
fuel? 

1.  The  perfect  combustion  of  the  fuel ;  and 

2.  The  best  possible  transmission  of  all  the  heat 
formed,  into  the  air  that  is  to  pass  into  the  rooms  of 
the  house. 

1463  How  is  the  first  of  these  requisites  obtained? 

By  having  a  good  draught  and  a  fire-box  which  is 
broad  and  shallow,  so  that  the  coal  shall  form  a  thin 
stratum  ;  by  which  arrangement  the  carbonic  acid  gas 
will  be  freely  formed,  and  pass  off  without  a  previous 
production  of  an  imperfectly  burnt  product. 

1464  How  is  the  second  of  these  requisites  attained  ? 

By  providing  a  great  quantity  of  surface  in  the  form 
of  pipes,  drums,  or  cylinders,  through  which  the  smoke 
and  hot  gases  must  pass  on  their  way  to  the  chimney, 
and  to  which  their  heat  will  be  imparted,  to  be  in  turn 
delivered  to  the  cold  and  pure  air  of  the  rooms  of  the 
house. 


CIIAPTEE  II. 

t 

COMBUSTION. 

1465  What  is  combustion  ? 

Every  species  of  combustion  with  which  we  are 
familiarly  acquainted  is  the  rapid  chemical  union  of  the 
oxygen  of  the  air  with  a  combustible  body,  attended 
with  the  evolution  of  light  and  heat. 

1466  flow  may  combustion,  as  we  ordinarily  see  it,  be  regarded  ? 

It  may  be  regarded  as  simply  &  process  of  oxidation. 

1467*   What  do  we  mean  by  the  term  oxidation  f 


SCIENCE   OF   COMMON   THINGS.  221 


Matter  not  destroyed  by  combustion.  Heat,  how  originated  by  combustion. 

The  combination  of  some  substance  with  oxygen, — - 
or  the  act  of  combining  with  oxygen. 

1468  Js  there  not  always  an  increase  in  weight  during  the  combustion 
of  inflammable  materials,  rather  than  a  loss  f 

The  products  of  combustion  always  exceed  the  weight 
of  the  original  substance  burned,  by  an  amount  equal 
to  the  weight  of  the  oxygen  gas  absorbed  during  the 
combustion. 

1469  What  becomes  of  the  oxidized  products  of  combustion  f 

They  for  the  most  part  combine  with  oxygen  to  form 
gases  and  vapors.  We  apply  to  these  products  the 
general  term  smoke. 

147*0    What  is  an  essential  requisite  to  every  process  of  combustion  f 

That  there  should  be  a  free  supply  of  air,  and  that 
the  products  of  combustion,  or  the  smoke,  should  be 
conducted  off. 

147*1  Why,  when  we  burn  a  candle  or  a  piece  of  wood  in  the  air,  does 
there  always  seem  to  be  a  loss  of  matter  f 

Because  the  results  of  combustion  in  these  cases  are 
either  gases  or  vapors,  the  existence  of  which,  not  being 
apparent  to  common  observation,  requires  to  be  made 
known  by  experiment. 

Until  nearly  the  close  of  the  last  century  it  was  generally  believed  and 
taught,  that  when  a  body  was  burned,  something  went  out  of  it, — that  it 
lost  weight.  Lavoisier,  a  celebrated  French  chemist,  overthrew  this  doc- 
trine by  burning  a  substance  in  connexion  with  an  arrangement  whereby 
all  the  results  or  products  of  the  combustion  were  saved.  These  on 
being  weighed  showed  a  gain  rather  than  a  loss,  the  amount  being  equal 
to  the  quantity  of  oxygen  which  had  been  absorbed  from  the  air  during 
the  process  of  combustion,  by  the  burning  substance  itself. 

147*3  How  is  heat  evolved  by  combustion  ? 

By  chemical  action.  As  latent  heat  is  liberated, 
when  water  is  poured  upon  lime,  by  chemical  action, 
so  latent  heat  is  liberated  in  combustion  by  chemical 
action  also. 

147*3    What  chemical  action  takes  place  in  combustion  f 

The  elements  of  the  fuel  combine  with  the  oxygen  of 
the  air. 

147*4  What  is  the  temperature  required  to  induce  the  combination  of 
oxygen  with  any  substance  called  ? 

10* 


222  SCIENCE   OF  COMMON   THINGS. 

The  burning  point — rust — flame — fire. 

The  burning  point. 

14*75  Is  this  point  different  for  different  substances  f 

It  is  ,'  thus  phosphorus  will  combine  slowly  at  77°  F., 
but  does  not  enter  into  rapid  combustion  until  the  tem- 
perature is  raised  to  104°  F.  Charcoal  burns  slowly 
below  a  red  heat. 

14*70  Is  the  quantity  of  heat  given  out,  when  a  body  combines  slowly 
with  oxygen,  the  same  as  when  it  combines  rapidly  with  it,  the  relative 
quantities  of  the  combining  bodies  remaining  the  same  in  both  cases  ? 

The  total  quantity  of  heat  given  out  is  the  same, 
whether  the  combustion  takes  place  slowly  or  quickly  ; 
but  in  the  case  of  slow  combustion,  the  heat  is  much 
less  intense,  and  often  becomes  insensible,  because 
during  the  long  time  occupied  in  combination  the 
greater  part  is  carried  away  by  conduction. 

147"7  Is  the  quantity  of  light  given  out  the  same,  whether  the  combus- 
tion be  rapid  or  slow  ? 

No  :  the  quantity  of  light  given  out  during  the  com- 
bination of  oxygen  with  a  given  quantity  of  a  com- 
bustible body  varies  greatly,  according  to  the  rapidity 
of  the  combustion. 

1478   What  is  rust  f 

The  oxidation  of  iron  in  moist  air. 

14*79   When  iron  rusts  in  the  air  is  heat  given  outf 

Certainly ;  but  the  process  of  rusting  takes  place  so 
slowly  that  the  amount  of  heat  given  out  at  any  one 
time  is  imperceptible  to  our  senses. 

148  O   What  is  flame  f 

Burning  gas  or  vapor. 

1481   What  is  fire? 

Heat  and  light  produced  by  the  combustion  of  in- 
flammable substances. 

1483  What  does  the  brightness  or  illuminating  power  of  flame  depend 
fnf 

It  depends  on  the  degree  of  heat  in  part,  but  mainly 
on  the  presence  or  absence  of  solid  particles  in  the 
flame,  which  may  act  as  radiating  points. 

1483  Are  there  solid  particles  in  every  illuminating  flume  t 


SCIENCE   OF   COMMON   THINGS.  223 

W  hen  will  a  lamp  smoke  ?  Benefit  of  glass  chimney  on  lamp. 


There  are  /  and  if  we  present  a  cold  surface  to  the 
flame,  they  become  deposited  on  it  in  the  form  of  soot. 

1484  When  we  Say  a  lamp  smokes,  what  do  we  mean  * 

That  the  solid  parts  of  the  flame  are  passing  off  in  an 
unconsumed  state, 

1485  When  the  flame  burns  properly,  why  does  the  smoke  cease  to  be 
emitted  f 

Because  the  solid  particles  of  carbon  constituting  the 
smoke  are  burned  up,  or  are  completely  united  with 
oxygen,  forming  an  invisible  gas — carbonic  acid. 

1480  From  what  source  is  the  carbon,  constituting  the  illuminating  par- 
ticles in  tiie  one  case  and  the  soot  in  the  other,  derived? 

It  was  originally  a  part  of  the  burning  or  combustible 
body, 

148  7   When  will  a  flame  smoke  f 

When  the  supply  of  oxygen  received  from  the  air  ig 
insufficient  to  consume  all  the  carbon  which  the  heat 
separates  from  the  combustible  body  in  the  form  of 
soot. 

1488  What  benefit  arises  from  surrounding  aflame  with  a  glass  cylin- 
der of  chimney  open  at  the  bottom  and  top  ? 

When  a  flame  burns  without  a  chimney,  the  hot  air 
radiates  in  all  directions  ;  but  when  it  is  surrounded 
by  a  chimney,  the  hot  air  is  confined  within  the  walls 
of  the  cylinder:  consequently,  the  hot  air  will  issue 
rapidly  from  the  top  of  the  chimney,  and  cold  air  will- 
enter  equally  fast  at  the  bottom  to  replace  it.  In  this 
Way  a  constant  current  of  fresh  air  is  kept  up  through 
the  centre  of  the  flame,  causing  a  more  perfect  com- 
bustion, and  a  brighter  and  stronger  flame. 

148Q  Why  in  solar  and  astral  lamps  do  we  use  a  hollow  or  circular 
wick? 

In  order  that  a  current  of  air  may  rusn  up  through  the 
interior  surface  of  the  flame  as  well  as  aiong  the  exterior. 

1490   What  is  fuel? 

Any  substance  which  serves  as  aliment  or  food  for 
'(ire.  In  ordinary  language  we  mean  by  fuel  the  pecu- 
liar substance  of  plants,  or  the  products  resulting  from 


224  SCIENCE   OF   COMMON   THINGS. 

"What  is  fuel — carbon — charcoal — soot  ? 

their  decomposition,  designated  under  the  various  names 
of  wood,  peat,  and  coal. 

1401    What  are  the  constituents  of  wood? 

Carbon,  hydrogen,  and  oxygen,  combined  together, 
make  up  the  chief  part  of  its  bulk  ;  all  wood  also  con- 
tains water. 

1403    What  is  hydrogen? 

It  is  an  inflammable  gas,  one  of  the  elements  of  which 
water  is  composed.  The  gas  used  in  our  streets  is  in 
great  part  hydrogen.  Hydrogen,  when  pure,  has  neither 
taste  nor  odor. 

1403  What  are  the  peculiar  characteristics  of  hydrogen  gast 

1.  It  is  the  lightest  of  all  known  substances  ; 

2.  It  will  burn  immediately  on  being  ignited ;  and 

3.  A  lighted  candle  (immersed  in  this  gas)  will  be 
instantly  extinguished. 

1404  What  is  carbon  f 

A  solid  elementary  substance,  generally  of  a  dark  or 
black  color,  well  known  under  the  forms  of  charcoal, 
lampblack,  coke,  etc. 

1405  What  is  charcoal? 

"Wood  which  has  been  exposed  to  heat  until  it  has 
been  deprived  of  all  its  gases  and  volatile  parts. 

1406  Can  all  animal  and  vegetable  substances,  by  partial  burning,  be 
converted  into  coal  f 

They  can. 

1407*  In  the  charring  of  animal  and  vegetable  substances,  do  we  gene- 
rate charcoal,  or  did  it  exist  there  before  % 

The  carbon  or  coal  existed  there  previously,  though 
in  chemical  combination  with  other  bodies,  which  are 
principally  driven  off  by  heat,  as  is  apparent  from  the 
fact  that  a  charred  body  weighs  much  less  than  the 
original  substance ;  animal  and  vegetable  substances 
consist,  therefore,  in  part  of  coal. 

1408    Wliatissoot? 

Coal  in  a  state  of  minute  division,  which  is  deposited 
from  the  flame  of  bituminous  or  pit-coal,  wood,  oil, 


SCIENCE   OF  COMMON   THINGS.  225 

How  charcoal  is  prepared.  "What  is  mineral  coal. 

resin,  etc.,  when,  during  the  combustion  of  these  sub- 
stances, there  is  an  insufficient  supply  of  air. 

1499  How  is  charcoal  prepared  f 

By  charring  wood  in  mounds  or  pits,  covered  with 
turf  or  soil  in  such  a  way  as  to  exclude  in  a  great  degree 
the  admission  of  air,  and  thus  prevent  complete  com- 
bustion. 

1500  What  is  mineral  or  hard  coal? 

Coal  is  the  product  of  a  vast  accumulation  of  vege- 
table matter,  deposited  during  a  remote  geological 
period  in  beds  or  layers  in  the  earth,  and  which,  by  the 
action  of  pressure,  heat,  and  other  causes,  has  become 
consolidated  and  hardened  into  its  present  form. 

15  Ol  How  does  the  coal  occur  in  the  earth  ? 

In  strata  or  layers,  varying  from  a  few  inches  to 
several  feet  in  thickness,  inclosed  between  other  strata 
of  limestone,  clay,  or  iron  ore. 

15OS  In  what  manner  is  it  supposed  that  this  great  accumulation  of 
vegetable,  material  took  place  1 

The  vegetable  matter  of  which  coal  is  composed  is 
supposed,  by  some,  to  have  grown  in  immense  swamps 
or  marshes.  By  others,  the  vegetable  matter  is  sup- 
posed to  have  been  swept  down  ~by  rivers,  and  deposited 
at  their  mouths  or  estuaries  in  immense  beds. 

1503  Are  such  accumulations  of  vegetable  matter,  through  the  agency 
of  rivers,  going  on  at  the  present  day  ? 

At  the  present  time  the  Red  River  of  Texas  is  abso- 
lutely choked  up  with  a  raft  composed  of  trunks  of 
trees  and  other  vegetable  matter,  many  miles  in  extent, 
and  of  unknown  thickness.  Other  rivers  of  the  South- 
western United  States  bring  down  vegetable  materials 
annually,  sufficient  for  the  production  of  vast  beds  of 
coal. 

1504  How  do  we  know  that  coal  is  all  vegetable  matter  ? 

Because  in  every  coal  mine  we  find  the  leaves, 
trunks,  and  fruits  of  trees  in  immense  numbers,  many 
of  them  in  a  most  perfect  state  of  preservation ;  so 
much  eo,  that  the  botany  of  the  coal  period  can  be 


226  SCIENCE   OF   COMMON   THINGS. 

Difference  between  anthracite  and  bituminous  coal. 

studied  with  nearly  as  great  ease  and  facility  as  the 
botany  of  any  given  section  of  the  present  surface  of 
the  earth. 

1505  What  occasions  the  difference  between  bituminous  and  anthracite 
coal? 

Bituminous  coal  contains  a  large  amount  of  bitumen 
and  other  pitchy  volatile  substances  which  readily 
ignite  and  burn  with  smoke  and  flame.  In  anthracite 
coal  these  substances  have  been  driven  out ;  it  is  there- 
fore a  purer  variety  of  carbon,  and  burns  without  smoke 
or  flame. 

1506  Are  the  deposits  of  coal  of  very  great  extent  f 

They  are  ;  mineral  coal  exists  in  all  the  great  divi- 
sions of  the  earth.  The  largest  deposits  of  coal,  how- 
ever, occur,  in  the  United  States,  in  Pennsylvania  and 
the  Yalley  of  the  Mississippi. 

1507  Why  will  not  stones  do  for  fuel  as  well  as  coal  f 

Because  they  contain  no  hydrogen,  and  little  or  no 
carbon. 

1508  Of  what  are  oil,  tallow,  and  wax  composed  t 

Principally  of  carbon  and  hydrogen  gas.  The  solid 
part  is  carbon,  the  volatile  part  is  hydrogen  gas. 

1509  At  what  period  of  the  year  does  wood  contain  the  greatest  amount 
of  water  ? 

In  the  spring  and  summer,  when  the  sap  flows  freely 
and  the  influence  of  vegetation  is  the  greatest. 

1510  Why  is  wood  generally  cut  in  the  winter  season  f 

Because  at  that  season  there  is  but  little  sap  in  the 
tissues,  and  the  wrood  is  drier  than  at  any  other  period. 

1511  Why  is  it  difficult  to  inflame  coal  or  hard  wood  with  the  blaze  of 
a  match  f 

Coal  and  hard  wood  on  account  of  their  density  are 
good  conductors,  and  carry  off  the  heat  of  the  kindling 
substance,  so  as  to  extinguish  it,  before  they  themselves 
become  raised  to  the  temperature  necessary  for  their 
combustion. 

1513   Why  is  it  easy  to  ignite  light  fuel  with  a  smatt  blaze  f 

Light  fuel  being  a  slow  conductor  of  heat  kindles 


SCIENCE  OF  COMMON   THINGS.  227 

Amount  of  water  in  green  and  dry  wood.  Weight  of  wood. 

easily,  and,  from  the  admixture  of  atmospheric  air  in  its 
pores  and  crevices,  burns  out  rapidly,  producing  a  com- 
paratively temporary,  though  often  strong  heat. 

1513  In  recently  cut  wood,  what  proportion  of  its  weight  is  water  ? 

From  one-fifth  to  one-half. 

1514  After  wood  has  been  dried  in  the  air  for  ten  or  twelve  months, 
how  much  water  does  it  usually  contain  ? 

From  twenty  to  twenty-Jive  per  cent. 

1515  Why  do  we  call  some  woods  hard,  and  others  soft  f 

This  distinction  is  grounded  upon  the  facility  with 
which  they  are  worked,  and  upon  their  power  of  pro- 
ducing heat.  Hard  woods,  as  the  oak,  beech,  wTafnut, 
elm,  and  alder,  contain  in  the  same  bulk  more  solid 
fibre,  and  their  vessels  are  narrower  and  more  closely 
packed  than  those  of  the  softer  kinds,  such  as  pine, 
larch,  chestnut,  etc. 

1516  How  many  pounds  avoirdupois  are  there  in  a  cord  of  dry,  hard 
wood? 

From  forty-four  hundred  pounds  in  a  cord  of  dry 
hickory,  to  twenty-six  hundred  in  a  cord  of  dry,  soft 
maple. 

151*7    What  is  the  most  valuable  wood  for  fuel?  , 

The  varieties  of  hickory ;  after  that,  in  order,  the 
oak,  the  apple-tree,  the  white-ash,  the  dog-wood,  and  the 
leech. 

1518  What  woods  give  out  the  least  heat  in  burning  f 

The  white-pine,  white-birch,  and  poplar. 

1519  Why  is  it  unprofitable  to  burn  green  wood  or  wet  coal  f 

It  is  a  well-known  law  of  heat  that  the  evaporation 
of  liquids,  or  their  conversion  into  steam,  consumes  or 
renders  latent  a  great  amount  of  caloric.  When  green 
wood  or  wet  coal  are  added  to  the  fire,  they  abstract 
from  it  by  degrees  a  sufficient  amount  of  heat  to  con- 
vert their,  own"  sap  or  moisture  into  steam  before  they 
are  capable  of  being  burnt.  As  long  as  any  consider- 
able part  of  this  fluid  remains  unevaporated,  the  com- 
bustion goes  on  slowly,  the  fire  is  dull,  and  the  heat 
feeble. 


228  SCIENCE  OF  COMMON  THINGS. 

Unprofitable  to  burn  green  wood.        Chemical  changes  produced  by  combustion. 

1530  Js  there  any  truth  in  the  remark  often  made  "  that  it  is  economy 
to  burn  green  wood  because  it  is  more  durable,  and  therefore  in  the  end  more 
cheap  ?" 

No  j  it  is  true  that  the  consumption  of  green  wood 
is  less  rapid  than  dry,  but  to  produce  a  given  amount 
of  heat,  a  far  greater  amount  of  fuel  must  be  con- 
sumed. 

1531  Jn  ordinary  fuel,  what  three  elements  enter  into  the  process  of 
combustion  f 

Hydrogen  gas,  carbon.,  and  oxygen  gas;  the  two 
former  in  the  fuel,  and  the  latter  principally  in  the  air 
which  surrounds  the  fuel. 

1533  What  chemical  changes  in  air  and  fuel  are  produced  by  com- 
bustion ? 

1.  Some  of  the  oxygen  of  the  air,  combining  with  the 
hydrogen  of  the  fuel,  forms  vapor  of  water  ;  and 

2.  Some  of  the  oxygen  of  the  air,  combining  with  the 
carbon  of  the  fuel,  forms  carbonic  acid  gas. 

1523  Why  is  there  more  smoke  when  fresh  fuel  is  added  than  when  the 
fuel  is  red  hot  ? 

Because  more  carbon  and  volatile  matters  are  sepa- 
rated from  the  fuel  than  can  be  reduced  by  combustion  / 
and  the  surplus  flies  off  in  smoke. 

1534  Why  is  there  so  little  smoke  with  a  red-hot  fir ef 

Because  the  entire  surface  of  the  coals  is  in  a  state  of 
combustion ;  and,  as  very  little  of  the  escaping  carbon 
remains  unconsumed,  there  is  but  little  smoke. 

1535  When  a  coal  fire  is  lighted,  why  are  paper  and  wood  laid  at  the 
bottom,  against  the  grate  f 

That  the  flame  may  ascend  through  the  fuel  to  heat 
it.  If  the  fire  were  kindled  from  the  top,  the  flame 
would  not  come  in  contact  with  the  fuel  placed  below. 

1536  Why  do  we  cover  up  afire  with  ashes  or  cinders  to  preserve  it  f 

The  covering  of  ashes  or  cinders  protects  the  fire 
from  the  action  of  the  air,  and  when  fuel  is  deprived  of 
air  it  ceases  to  burn. 

1537  Why  does  afire  burn  so  fiercely  in  windy  weather  ? 

Because  the  air  is  rapidly  changed,  and  affords 
plentiful  nourishment  to  the  fire. 


SCIENCE    OF   COMMON   THINGS.  229 

"Why  water  extinguishes  a  fire.  Cause  of  the  heat  of  a  dunghill. 

15SS    Why  does  a  pair  of  bellows  aid  in  kindling  afire  ? 

Because  it  drives  the  air  more  rapidly  to  theft-re,  and 
the  plentiful  supply  of  oxygen  soon  makes  the  tire  burn 
intensely. 

15S9    Why  does  water  extinguish  a  fire  1 

1.  Because  the  water  forms  a  coating  over  the  fuel, 
which  keeps  it  from  the  air  ;  and 

2.  The  conversion  of  water  into  steam  draws  off  the 
heat  of  the  burning  fuel. 

1530  Why  does  a  Uast  of  air  from  a  pair  of  bellows  often  extinguish  a 
red-hot  coal  of  anthracite  ? 

Because  the  cold  air  absorbs  the  heat  of  the  coal  so 
quickly  that  it  extinguishes  it. 

1531  Why  can  you  not  light  a  candle  or  lamp  with  a  match  so  long  as 
the  sulphur  on  the  end  of  it  is  burning  f 

The  chemical  reason  for  this  well  known  fact  is,  that 
the  sulphurous  acid,  formed  by  combustion  of  sulphur 
in  the  air,  surrounds  the  wick,  and  abstracts  the  oxygen 
from  the  air,  by  passing  to  a  higher  state  of  oxidation  ; 
and  this  heavy  vapor  hangs  about  the  wick  and  excludes 
the  air. 

153S   Cannot  wood  be  made  to  blaze  without  actual  contact  with  fire? 

Yes  ;  if  a  piece  of  wood  be  held  near  the  fire  for  a 
little  time,  it  will  blaze,  even  though  it  does  not  touch 
the  fire. 

1533  Why  will  wood  blaze,  even  if  it  does  not  touch  the  fire  ? 

Because  the  heat  of  the  fire  drives  out  the  inflam- 
mable gas  of  the  wood,  which  gas  is  ignited  by  contact 
with  the  red-hot  coals. 

1534  What  causes  the  heat  of  fire  1 

The  carbon  of  fuel  (when  heated)  combines  with  the 
oxygen  of  the  air,  and  produces  carbonic  acid  gas. 
Again,  the  hydrogen  of  the  fuel  combining  with  other 
portions  of  oxygen,  condenses  into  water ;  by  which 
chemical  actions  heat  is  evolved. 

1535  Whence  does  the  heal  of  a  dunghill  arise  f 

As  the  strawy  etc.,  of  the  dunghill  decays,  it  under- 


230  SCIENCE   OF   COMMON   THINGS. 

Benefit  of  stirring  a  dull  fire.  How  to  extinguish  a  chimney  on  fire. 

goes  fermentation,  which  produces  carbonic  acid  gas  / 
and  heat  is  evolved  through  a  species  of  combustion. 

153G   On  what  does  the  intensity  of  fire  depend  ? 

The  intensity  of  fire  is  always  in  proportion  to  the 
quantity  of  oxygen  with  which  it  is  supplied. 

1537  Why  does  stirring  a  dull  fire  serve  to  quicken  it  ? 

Because  it  breaks  up  the  compacted  cinders  and 
coals,  making  a  passage  for  the  air  into  the  very  heart 
of  the  fire. 

1538  Why  is  the  fiame  of  a  candle  extinguished  when  bloion  by  the 
breath,  and  not  made  more  intense,  like  a  fire  f 

Because  the  flame  of  a  candle  is  confined  to  a  very 
small  wick,  from  which  it  is  severed  by  the  breath,  and 
(being  unsupported)  must  go  out. 

1539  When  a  chimney  with  an  open  fireplace  gets  on  fire,  and  burns  so 
as  to  endanger  the  house,  how  may  it  at  once  be  extinguished? 

By  throwing  a  quantity  of  brimstone  or  sulphur  into 
the  fire,  and  closing  up  the  fireplace  with  a  fireboard  or 
screen.  The  sulphurous  acid  soon  fills  the  chimney,  and 
taking  up  all  the  oxygen  from  the  contained  air,  ex- 
tinguishes the  fire.  Even  the  fire,  after  it  has  extended 
into  the  woodwork  of  the  house,  may  be  extinguished 
by  this  simple  method. 

1540  Fire  in  a  chimney  may  be  also  extinguished  by  closing  the  top  of 
thefiue  with  a  damper :  how  does  this  extinguish  the  fire  f 

It  cuts  off  the  draught,  and  the  carbonic  acid  gene- 
rated by  the  combustion  soon  puts  an  end  to  the  fire. 

1541  What  is  meant  by  spontaneous  combustion  ? 

Combustion  produced  without  contact  with  fire  or 
flame. 

1543   Give  me  an  example  of  spontaneous  combustion. 

Oiled  cotton  and  rags  imbued  with  any  drying  oil, 
when  packed  in  mass  in  a  barrel,  take  fire,  after  a  time, 
at  ordinary  temperatures.  Mixed  lampblack  and  lin- 
seed-oil cake  take  fire  at  ordinary  temperatures,  if  the 
lampblack  is  in  excess,  or  a  portion  of  it  is  dry. 

1543   What  is  generally  the  cause  of  spontaneous  combustion  ? 

The  absorption  of  oxygen.     Porous  bodies,  that  are 


SCIENCE   OF   COMMON   THINGS.  231 

Why  all  flames  are  not  equally  luminous.  Cause  of  the  color  of  a  fire. 

at  the  same  time  bad  conductors  of  heat,  by  the 
absorption  of  oxygen  may  become  red  hot,  and  finally 
burst  into  a  flame. 

1544  Is  pine  charcoal  capable  of  taking  fire  at  an  extremely  low  tem- 
perature ? 

Porous  bodies,  like  pine  charcoal,  when  perfectly 
dry,  absorb  oxygen  rapidly  from  the  air,  and  take  fire 
at  a  temperature  below  212°  Fahrenheit,  or  the  boil- 
ing-point of  water. 

This  has  been  proved  by  actual  experiment,  a  piece  of  light  pine  char- 
coal taking  fire  on  a  surface  of  sheet  iron,  heated  below  the  boiling-point 
of  water. 

1545  Why  are  not  all  flames  equally  luminous  t 

In  all  flames,  the  light  is  mainly  emitted  from  mi- 
nute particles  of  matter,  intensely  heated,  and  floating 
in  the  burning  gas  or  vapor  ;  and  hence  a  flame  con- 
taining few  such  particles,  will  emit  but  a  feeble  light, 
even  though  its  temperature  is  very  great. 

1546  Upon  what  fact  does  the  production  of  artificial  light  depend  ? 

Upon  the  fact  that  at  certain  high  temperatures  all 
matter  becomes  luminous. 

3-547  In  order  that  we  may  profitably  use  a  combustible  body  for  illu- 
minating purposes,  what  is  required  of  the  products  of  the  combustion  f 

That  they  should  be  volatile,  and  freely  escape  from 
the  immediate  vicinity  of  the  illuminating  centre. 

1548  The  product  of  all  the  ordinary  forms  of  combustion  is  a  gas — 
carbonic  acid :  what  would  have  been  the  result  if  the  product  of  every  com- 
bustion had  been  a  permanent  solid  ? 

The  world  would  have  been  buried  beneath  its  own 
ashes. 

1549  Why  is  the  flame  of  an  ordinary  fire  ydloto  f 

Because  the  heat  is  not  sufficient  to  render  the  car- 
bon white  hot.  Increase  the  intensity  of  combustion, 
arid  the  color  of  the  burning  bodies  or  the  flames  rises 
from  red  to  yellow,  and  from  yellow  to  white. 

1550  A  candle  burns  when  lighted :  explain  how  this  is  1 

The  heat  of  the  lighted  wick  decomposes  the  tallow 
into  its  elementary  constituents,  hydrogen  and  carbon. 
The  hydrogen  is  nrst  consumed  as  a  gas  by  itself  with 


232  SCIENCE   OF   COMMON   THINGS. 


Phenomena  of  combustion  in  the  flame  of  a  candle. 


an  almost  imperceptible  light,  but  with  a  powerful 
evolution  of  heat;  this  causes  the  carbon,  simultane- 
ously eliminated,  to  become  incandescent  and  conse- 
quently luminous. 

1551  As  more  carbon  is  successively  -eliminated,  what  becomes  of  it  ? 

The  moment  the  incandescent  floating  carbon  comes 
to  the  edge  of  the  flame,  it  finds  the  oxygen  of  the  air, 
unites  with  it,  and  becomes  converted  into  the  invisible 
gas,  carbonic  acid,  while  its  place  is  occupied  immedi- 
ately by  another  portion  of  solid  carbon. 

1553    What  if  there  is  not  sufficient  oxygen  to  consume  the  carbon  1 

It  then  passes  off  as  soot,  and  we  say  the  candle 

smokes. 

1553  Where  is  the  tallow  or  wax  of  a  candle  decomposed  f 

In  the  wick.  The  melted  tallow  or  wax  rises  up  the 
wick  by  capillary  attraction,  and  is  rapidly  decom- 
posed by  the  heat  of  the  flame. 

1554  Of  what  three  parts  does  the  flame  of  every  lamp  or 
candle  consist  ? 

The  flame  of  every  lamp  or  candle  consists 
of  three  cones.  The  innermost  cone  (a,  Fig. 
49)  consists  of  gaseous  matter  produced  by  the 
decomposition  of  the  tallow ;  this  is  at  a  tem- 
perature below  redness.  Around  it  is  the  lu- 
minous cone  (b\  consisting  of  burning  hydro- 
gen, in  which  the  particles  of  carbon  float  at  a 
white  heat ;  and  on  the  very  outside  (c),  a 
thin,  hardly-perceptible  veil  in  which  carbon 
is  burning.  The  veil  is  of  a  blue  color,  most 
plainly  seen  at  the  bottom  of  the  flame. 

1555  Which  is  the  hottest  part  of  thejlame  f 

The  pale  Hue  flame  ;  this  marks  the  point  where 
the  combination  of  the  oxygen,  supplied  from  without, 
with  the  combustible  matter  evolved  from  the  interior 
takes  place. 

155G    Why  does  thejlame  of  a  candle  point  upwards  ? 

Because  it  heats  the  surrounding  air,  which 


SCIENCE   OF   COMMON   THINGS.  233 

Use  of  a  hole  in  the  top  of  a  lamp.        Use  of  ground  glass  lamp  shades. 

hot)  rapidly  ascends,  driving  the  flame  upwards  at  the 
same  time. 

1557*  Why  does  the  hand,  held  above  a  candle,  suffer  more  from  heat 
than  when  it  is  placed  below  the  flame,  or  on  one  side  of  it  t 

Because  the  hot  gases  and  air  (in  their  ascent)  come 
in  contact  with  the  hand  placed  above  the  flame ;  but 
when  the  hand  is  placed  below  the  flame,  or  on  one 
side,  it  only  feels  heat  from  radiation. 

1553   Why  is  not  the  wick  of  a  candle  consumed  f 

The  wick,  although  it  is  blackened  by  the  heat,  is 
prevented  from  consuming,  merely  because  it  is  sur- 
rounded by  inflammable  vapor,  so  that  the  oxygen  of 
the  atmosphere  has  no  access  to  it. 

1559  Why  do  att  closed  lamps  require  a  small  hole  in  the  top  f 

To  admit  the  air  •  otherwise  the  pressure  of  the 
atmosphere  will  prevent  the  oil  from  ascending  the 
wick ;  if  the  hole  be  obstructed,  the  oil  will  sometimes 
overflow  from  the  expansion  of  the  confined  air. 

1560  Why  do  we  use  ground-glass  globes  for  lamp  shades  ? 

To  relieve  the  eye  from  the  glare  of  light.  Ground- 
glass  shades  have  the  effect  to  disperse  the  rays  by  the 
numerous  reflections  and  refractions  wThich  they  occa- 
sion ;  until  at  length  the  light  issues  from  all  parts  of 
their  surface,  and  it  appears  as  though  the  glass  itself 
were  the  luminous  body. 


CHAPTER    III. 

RESPIRATION    AND    NUTRITION. 
15 SI   What  is  respiration? 

The  act  of  inhaling  air  into  the  lungs,  and  again 
expelling  it. 


234:  SCIENCE    OF   COMMON    THINGS. 

Combustion  a  form  of  respiration.  Construction  of  the  lungs. 

1562  What  is  the  object  of  drawing  air  into  the  lungs  and  again  expel- 
ling it  ? 

To  oxidize  the  carbon  and  hydrogen  of  the  blood. 

1563  We  receive  into  the  lungs  oxygen  through  the  medium  of  the  atmo- 
sphere, mingled  with  nitrogen :  what  do  we  expel  from  the  lungs  f 

The  nitrogen  returns  unaltered ;  the  oxygen  unites 
with  the  carbon  of  the  blood  to  form  a  gas — carbonic 
acid,  and  with  hydrogen  to  form  the  vapor  of  water. 

1564  Are  not  these  the  same  products  of  every  ordinary  form  of  com- 
bustion f 

They  are  ;  therefore  respiration  or  breathing  is  but 
a  form  of  combustion. 

1565  It  is  estimated  that  a  man  receives  into  his  system  about  eight 
hundred  pounds  of  oxygen  from  the  atmosphere  in  a  year,  but  his  weight  at 
the  end  of  the  year  has  increased  but  little,  or  not  at  all :  what  becomes  of  all 
this  oxygen  ? 

No  part  of  it  remains  in  the 'body,  but  is  given  out 
again,  combined  with  carbon  and  hydrogen. 

1566  How  much  carbon  passes  out  of  the  system  of  an  adult  man  by 
the  agency  of  respiration  daily  ? 

About  fifteen  ounces. 

1567  How  is  this  great  abstraction  of  material  from  the  body  made  up  T 

By  the  food  which  we  eat. 

1568  What  are  the  lungs  ? 

Lungs  are  made  up  of  bloodvessels  imbedded  in  a 
fleshy  substance  which  we  denominate  cellular  tissue, 
and  expanded  over  the  walls  of  a  series  of  chambers  or 
cavities. 

They  are  so  situated  in  the  thorax  (or  chest)  that  the  air  must  enter 
into  them  whenever  the  cavities  of  the  thorax  are  enlarged.  The  process 
of  breathing  is  performed  thus :  When  we  INHALE,  the  thorax  (or  chest) 
is  expanded ;  in  consequence  of  which  a  vacuum  is  formed  round  the 
lungs,  and  the  heavy  external  air  instantly  enters  (through  the  mouth  and 
throat)  to  supply  this  vacuum. 

When  we  EXHALE,  the  thorax  contracts  again;  in  consequence  of 
which  it  can  no  longer  contain  the  same  quantity  of  air  as  it  did  before, 
and  some  of  it  is  necessarily  expelled.  When  this  expulsion  of  air  takes 
place,  the  lungs  and  muscular  fibres  of  the  windpipe  and  gullet  contract  in 
order  to  assist  the  process. 

1569  To  what  may  the  mechanism  of  the  lungs  in  respiration  be  con* 
pared  ? 

To  the  action  of  a  bellows. 


SCIENCE    OF    COMMON   THINGS.  235 


Necessity  of  cleanliness.  Color  of  the  blood. 

157*0  Do  we  respire  or  absorb  and  expel  oxygen  in  any  oilier  way  than, 
through  the  lungs  ? 

We  breathe  also  in  a  degree  through  the  pores  of 
the  skin,  absorbing  oxygen  and  expelling  carbonic  acid. 

157*1  Do  extensive  burns  on  the  surface  of  tht  body  frequently  produce 
diseases  of  the  lungs  f 

They  do. 

157*3  Why  should  extensive  burns  on  the  surface  of  the,  body  tend  to 
produce  diseases  of  the  lungs  ? 

While  in  a  condition  of  health,  the  skin  tranquilly 
aids  the  lungs  in  the  expulsion  of  carbonic  acid  from 
the  body  ;  but  the  portion  of  the  skin  which  has  been 
scorched  by  an  extensive  burn,  no  longer  being  able  to 
perform  that  function,  the  lungs  are  obliged  to  assume 
an  extra  duty,  and  suffer  as  a  consequence  of  their 
exertion. 

157*3  //j  by  neglect  of  washing,  we  suffer  the  sJcin  to  become  covered  with 
impurities,  do  we  not  disturb  the  healthy  action  of  the  system  f 

We  do  ;  there  is  no  better-established  law  of  health, 
than  that  the  surface  of  the  whole  body  should  be  kept 
clean  and  free  from  all  impurities. 

157*4  If  the  carbon  taken  from  the  system  through  the  agency  of  the 
lungs  be  not  t  estored,  what  is  the  consequence  ? 

Starvation  ensues. 

157*5  How  does  the  oxygen  we  inhale  mingle  with  the  blood? 

The  oxygen  of  the  air  is  absorbed  in  the  lungs  by  the 
blood,  and  imparts  to  it  a  bright  red  color. 

157*6  How  does  oxygen  convert  the  color  of  blood  into  a  bright  red  f 

The  coloring  matter  of  the  blood  is  formed  by  very 
minute  globules  floating  in  it.  The  oxygen  uniting 
with  these  globules  changes  their  color,  to  a  bright  red. 
The  blood  contains  iron,  and  this  metal  is  supposed  to 
play  an  important  part  in  the  coloration  of  the  blood. 

157*7*   What  color  is  the  blood  before  it  is  oxidized  in  the  lungs  ? 

A  dark  purple  ;  the  oxygen  turns  it  to  a  bright  red* 

157*  S  Do  plants  respire  as  well  as  animals  t 

They  do;  and  their  leaves  may  be  regarded  as  per- 
forming for  them  similar  offices  as  the  lungs  of  animals. 
They  are  the  breathing  organs  of  plants. 


SCIENCE    OF   COMMON    THINGS. 


How  water  plants  purify  the  water.  Cause  of  animal  beat. 

1579  Js  there  any  difference  between  the  respiration  of  plants  and 
animals  f 

The  process  of  respiration  in  plants  is  exactly  the 
reverse  of  that  in  animals.  Animals  absorb  oxygen,  and 
give  out  carlo  nic  acid  ;  plants,  on  the  contrary,  absorb 
carbonic  acid,  and  return  oxygen. 

15SO  It  is  estimated  that  the  population  of  London  adds  to  the  atmo- 
sphere daily.  4,  500,000  pounds  of  carbonic  acid:  how  is  this  immense  quan- 
tity of  deleterious  gas  removed  from  the  atmosphere  f 

Principally  through  the  agency  of  plants,  which 
absorb  it. 

1581  Do  water-plants  purify  and  free  water  from  carbonic  acid  in  the 
same  manner  that  land-plants  purify  the  atmosphere  ? 

The  respiration  of  fishes  produces  carbonic  acid,  and 
anless  this  is  removed  from  the  water,  animal  life  will 
cease  to  exist  in  it.  Water-plants  absorb  the  carbonic 
acid  from  the  water,  and  restore  the  oxygen. 

1583  During  bright  weather,  the  leaves  of  water-plants,  it  will  be  no- 
ticed, are  covered  with  little  bubbks  :  what  are  these  bubbles  1 

Oxygen  gas,  liberated  by  the  organs  of  the  plant. 

1583  It  is  good  policy,  in  fountains  and  reservoirs  of  water,  to  free 
them  wholly  from  the  presence  of  vegetable  and  animal  organisms  ? 

It  is  not  :  they  are  both  dependent  on  one  another, 
and  the  joint  action  of  the  two  serves  to  keep  the  water 
pure  and  wholesome. 

1584  What  is  the  cause  of  animal  heat? 

The  oxygen  of  the  atmosphere,  received  into  the  blood 
in  the  lungs,  and  circulated  throughout  every  part  of 
the  animal  body,  acting  upon  the  elements  of  the  food, 
is  the  chief  source  of  animal  heat. 

1585  Why  does  oxygen  received  into  the  blood  produce  heat  ? 

Through  the  medium  of  the  capillary  vessels  oxygen 
absorbed  from  the  atmosphere  unites  with  carbon  and 
hydrogen.  This  union  is  a  species  of  combustion,  and 
produces  heat  in  the  same  manner  as  when  oxygen 
unites  with  fuel  in  an  ordinary  fire. 

1586  What  are  the  capillary  vessels  f 

Minute  bloodvessels  or  tubes  as  small  as  hairs  run- 


SCIENCE   OF    COMMON   THINGS.  237 


Why  no  heat  In  the  hair.  Two  kinds  of  blood,  venous  and  arterial. 

ning  all  over  the  body  ;  they  are  called  capillary  from 
the  Latin  word  capillaris,  "  like  a  hair." 

1537*  Do  these  capillary  vessels  run  all  over  the  human  body  f 

Yes.  Whenever  Hood  flows  from  a  wound,  some 
vein  or  vessel  must  be  divided  ;  and  as  you  can  bring 
blood  from  any  part  of  the  body  by  a  very  slight 
wound,  these  little  vessels  must  run  through  every  part 
of  the  human  frame. 

1588  How  do  hydrogen  gas  and  carbon  get  into  these  very  small 
vessels  ? 

The  food  we  eat  is  converted  into  blood,  and  blood 
contains  both  hydrogen  and  carbon. 

1580  Does  this  combustion,  and  the  consequent  production  of  animal 
heat,  take  place  in  every  part  of  the  body  ? 

In  the  animal  body,  heat  is  produced  only  in  those 
parts  to  which  arterial  Hood,  and  with  it  the  oxygen 
absorbed  in  respiration,  is  conveyed. 

1590  Why  is  there  no  heat  developed  in  hair,  wool,  andfeaffiers  f 

Because  they  receive  no  arterial  Hood,  and  therefore 
in  them  no  heat  is  developed. 

1591  What  two  kinds  of  blood  are  tliere  in  the  animal  body  ? 

Arterial  Hood  and  venous  Hood. 

159 S   What  is  the  difference  between  the  two? 

The  arterial  blood  going  from  the  lungs  conveys  the 
oxygen  which  it  has  absorbed  in  the  lungs  to  the  capil- 
lary vessels.  In  these  the  combustion  takes  place,  and 
the  color  of  the  blood  changes  from  a  bright  to  a  dark 
red  color. 

1593  What  becomes  of  the  blood  after  it  has  given  up  its  oxygen  to  the 
hydrogen  and  carbon  in  the  capillary  vessels  f 

It  enters  the  veins,  carrying  with  it  the  products  of 
combustion.  The  venous  blood  passes  to  the  lungs, 
throws  off  the  products  of  combustion,  absorbs  more 
oxygen,  becomes  converted  into  arterial  blood,  with 
a  renewal  of  color,  and  is  again  returned  into  the 
system. 

1594  What  becomes  of  the  carbonic  acid  gas  formed  in  the  human 
blood  ? 

11 


238  SCIENCE   OF   COMMON  (THINGS. 

Why  a  dead  body  is  cold.  "Why  we  perspire. 

The  lungs  throw  off  almost  all  of  it  into  the  air,  by 
the  act  of  respiration. 

1595  Does  the  heat  of  the  human  body  arise  from  the  same  cause  as 
the  heat  of  fire  ? 

Yes,  precisely.  The  carbon  of  the  blood  combines 
with  the  oxygen  of  the  air  inhaled,  and  produces  car- 
bonic acid  gas,  which  action  developes  heat. 

;     1590  If  animal  heat  is  produced  by  combustion,  why  does  not  the 
human  body  burn  up  like  a  coal  or  candle  ? 

It  actually  does  so.  Every  muscle,  nerve,  and  organ 
of  the  body  actually  wastes  away  like  a  burning  candle  • 
and  (being  reduced  to  air  and  ashes)  is  rejected  from 
the  system  as  useless. 

1597  If  every  bone,  muscle,  nerve,  and  organ  is  thus  consumed  by  com- 
bustion,  why  is  not  the  body  entirely  consumed? 

It  would  be  so,  unless  the  parts  destroyed  were  per- 
petually renewed ;  but  as  a  lamp  will  not  go  out  so  long 
as  it  is  supplied  with  fresh  oil,  neither  will  the  body  be 
consumed  so  long  as  it  is  supplied  with  sufficient  food. 

1598  What  is  the  principal  difference  between  the  combustion  of  a  fire 
or  lamp,  and  that  of  the  human  body  ? 

In  the  human  body,  the  combustion  is  effected  at  a 
much  lower  temperature,  and  is  carried  on  more  slowly, 
than  it  is  in  a  lamp  or  fire. 

1599  Why  is  a  dead  body  cold? 

Because  air  is  no  longer  conveyed  to  the  lungs  after 
respiration  has  ceased ;  and  therefore  animal  heat  is 
no  longer  generated  by  combustion. 

1600  Why  do  we  perspire  when  very  hot  ? 

The  pores  of  the  body  are  like  the  safety-valves  of  a 
steam-engine  ;  when  the  heat  of  the  body  is  very  great, 
some  of  the  combustible  matter  of  the  blood  is  thrown 
off  in  perspiration,  and  the  heat  of  the  body  is  thereby 
reduced. 

1601  Why  does  exercise  make  us  warm  ? 

Because  we  inhale  air  more  rapidly  when  we  exer- 
cise, and  cause  the  blood  to  pass  more  rapidly  through 
the  lungs  in  contact  with  it. 


SCIENCE  OF   COMMON   THINGS.  2S9 

Starvation  and  its  effects.  Food  the  fuel  of  the  body. 

16OS   Why  does  inhaling  air  rapidly  make  the  body  feel  warm? 

Because  more  oxygen  is  introduced  into  the  body ; 
in  consequence  of  which  the  combustion  of  the  blood  is 
more  rapid,  the  blood  itself  more  heated,  and  every 
part  of  the  body  is  made  warmer. 

16O3   When  a  man  is  starved  what  part  of  the  body  goes  first  f 

First  the  fat,  because  it  is  the  most  combustible ; 
then,  the  muscles ;  last  of  all,  the  brain  ;  and  then  the 
man  dies,  like  a  candle  which  is  burnt  out. 

1QO4   Why  does  a  man  shrink  when  starved  f 

Because  the  capillary  fires  feed  upon  the  human 
body  when  they  are  not  supplied  with  food-fuel.  A 
starved  man  shrinks  just  as  a  fire  does  when  it  is  not 
supplied  with  fuel. 

1BO5   What  is  fuel  of  the  body  f 

Food  is  the  fuel  of  the  ~body.  The  carbon  of  the 
food,  mixed  with  the  oxygen  of  the  air,  evolves  heat 
in  the  same  way  that  a  fire  or  candle  does. 

16O0    Why  does  hard  work  produce  hunger  f 

Because  it  produces  quicker  respiration ;  by^  which 
means  a  larger  amount  of  oxygen  is  introduced  into  the 
lungs,  and  the  capillary  combustion  increased.  Hun- 
ger is  the  notice  (given  by  our  body)  to  remind  us  that 
our  food-fuel  must  be  replenished. 

16O7"  Why  do  persons  feel  lazy  and  averse  to  exercise  when  they  are 
half-starved  or  ill  fed  f 

Because  desire  for  muscular  action  ceases  when  the 
body  is  not  supplied  with  nutritious  food. 

ISO 8  Why  do  we  like  strong  meat  and  greasy  food  when  the  weather 
is  very  cold  ? 

Because  strong  meat  and  grease  contain  large  pro- 
portions of  carbon  and  hydrogen,  which  (when  burned 
in  the  blood)  produce  a  larger  amount  of  heat  than  any 
other  kind  of  food. 

1SO0  Why  are  the  Esquimaux  so  passionately  fond  of  train  oil  and 
whale  blubber  f 

Because  oil  and  blubber  contain  large  quantities  of 
carbon  and  hydrogen,  which  are  exceedingly  combus- 


240  SCIENCE   OF   COMMON   THINGS. 

Activity  disagreeable  in  warm  weather. 

tible ;  and  as  these  people  live  in  climates  of  intense 
cold,  the  heat  of  their  bodies  is  increased  by  the  greasy 
nature  of  their  food. 

1610  Why  do  we  feel  lazy  and  averse  to  activity  in  very  hot  weather  1 

Because  muscular  activity  inweases  the  heat  of  our 
body  by  quickening  respiration,  and  lessens  our  desire 
for  active  exertion. 

1611  How  much  more  carbon  do  we  throw  off  from  the  system  by  respi- 
ration in  winter  than  in  summer  f 

Full  one-eighth  more. 


SCIENCE   OF   COMMON   THINGS.  241 

What  is  light  ?  Light  possesses  no  weight. 

PAET  VII. 

LIGHT,   AND  HOW  WE  SEE. 


CIIAPTEE   I. 

NATURE   AND   LAWS    OF    LIGHT. 

ISIS  Through  what  agency  alone  are  we  enabled  to  enjoy  the  sense  of 
sight  f 

Through  the  agency  of  light. 

1613  What  is  light? 

Light  is  now  believed  to  be  caused  by  the  agitation, 
vibration,  or  undulation  of  an  elastic  fluid  which  is  sup- 
posed to  occupy  and  pervade  all  space.  "We  call  this 
supposed  fluid  ether,  and  its  undulations  or  vibrations, 
reaching  the  eye,  affect  the  optic  nerve,  and  produce 
the  sensation  which  we  call  light. 

1614  What  analogy  is  there  between  the  eye  and  the  ear  f 

The  vibrations  or  undulations  of  the  ether  pass  along 
the  space  intervening  between  the  visible  object  and 
the  eye  in  the  same  manner  that  the  undulations  of  the 
air,  produced  by  a  sounding  body,  pass  through  the 
air  between  this  body  and  the  ear. 

1615  If  we  collect  a  large  quantity  of  light  in  one  point  by  means  of  a 
glass,  and  throw  it  upon  the  most  sensitive  balance,  does  it  indicate  any  per- 
ceptible weight  f 

It  does  not,  in  the  slightest  degree. 

1616  What  are  the  chief  sources  of  light? 

The  sun,  the  stars,  ftre  or  combustion,  electricity,  and 
phosphorescence. 

1617  With  what  velocity  does  light  move  through  space  1 


24:2  SCIENCE   OF   COMMON   THINGS. 

Velocity  of  light  Why  some  surfaces  are  brilliant  and  others  dull. 

With  a  velocity  of  one  hundred  and  ninety-two  thou- 
sand miles  in  a  second  of  time. 

1618  Does  all  light  travel  equally  fast? 

Yes ;  the  light  of  the  sun,  the  light  of  a  candle,  or 
the  light  from  houses,  trees,  and  fields. 

1619  How  long  a  time  does  it  require  for  light  to  pass  from  the  sun  to 
the  earth  f 

Eight  minutes  and  thirteen  seconds. 

102 O  How  much  time  is  required  for  a  ray  of  light  to  traverse  the 
space  intervening  between  the  nearest  fixed  stars  and  the  earth  f 

More  than  three  years  ;  and  from  the  farthest  nebulae 
hundreds  of  years  will  be  required. 

1621  What,   therefore,  would  be  the  consequence  if  one  oj  the  remote 
fixed  stars  were  to-day  "  blotted  from  the  heavens?" 

Several  generations  of  the  earth  would  pass  away 
before  the  obliteration  could  be  known  to  man. 

1622  In  wJiat  manner  do  the  moon  and  the  planets  give  light  f 

They  shine  only  by  means  of  the  surfs  light,  which 
is  reflected  from  their  surfaces. 

1623  Where  does  the  light  of  houses,  trees,  and  fields  come  from? 

The  light  of  the  sun  (or  of  some  artificial  light)  is  re- 
flected from  their  surfaces. 

1624  Why  are  some  surfaces  brilliant  (like  glass  and  steel)  and  others 
dull,  like  lead  ? 

Those  surfaces  which  reflect  the  most  light  are  the 
most  brilliant  /  and  those  which  absorb  light  are  dull. 

1625  How  does  the  velocity  of  light  compare  with  the  speed  of  a  loco- 
motive ? 

Light  passes  from  the  sun  to  the  earth  in  about  eight 
minutes  ;  a  locomotive  engine,  travelling  at  the  rate 
of  a  mile  in  a  minute,  would  require  upwards  of  one 
hundred  and  eighty  years  to  accomplish  the  same 
journey. 

1626  How  does  the  light  of  the  full  moon  compare  with  that  of  the  sun? 

It  is  estimated  to  be  three  hundred  thousand  times 
weaker  than  sunlight. 

1627  The  velocity   of  light  is  demonstrated  by   observations  on  the 
satellites  of  Jupiter.     Witt  you  explain  how  this  can  be  proved? 


SCIENCE   OF   COMMON   THINGS.  24:3 

Velocity  of  light  determined  from  observations  on  Jupiter's  satellites. 

The  earth  revolves  around  the  sun  in  an  orbit  of 
which  the  sun  is  the  centre.  We  are  able  to  calculate 
the  exact  time  when  an  observer  standing  in  the  centre 
of  the  earth's  orbit, — that  is,  in  the  sun,  would  see  an 
eclipse  of  Jupiter's  satellite ;  but  as  the  earth  moves 
round  the  sun  in  its  orbit,  it  is  brought  at  one  time 
ninety-five  million  of  miles  nearer  Jupiter  than  the  sun 
is,  and  at  another  time  it  is  carried  ninety-five  millions 
of  miles  further  off.  Now,  when  the  earth  is  nearest 
to  Jupiter,  the  eclipse  takes  place  eight  minutes  in 
advance  of  the  calculated  time,  and  when  it  is  ninety- 
five  millions  of  miles  farther  off,  the  eclipse  occurs  eight 
minutes  later  than  the  calculated  time.  This  delay  is 
occasioned  by  the  fact,  that  in  the  one  case  the  light 
coming  from  the  satellite  to  the  earth  has  to  traverse  a 
much  greater  distance  than  in  the  other ;  and  if  the 
light  requires  eight  minutes,  or  480  seconds,  to  move 
over  95,000,000  of  miles,  it  will  require  one  second  to 
move  over  197,000  miles,  or,  with  more  exact  data, 
192.000  miles  in  one  second. 


Fig.  50. 

The  explanation  above  given  will  be  made  clear  by  reference  to  the 
following  diagram,  Fig.  50.  S  represents  the  sun,  a  b  the  orbit  of  the 
earth,  and  T  T'  the  position  of  the  earth  at  different  and  opposite  points 
of  its  orbit.  J represents  Jupiter,  and  E,  its  satellite,  about  to  be  eclipsed 
by  passing  within  the  shadow  of  the  planet.  Now  the  time  of  the  com- 
mencement or  termination  of  an  eclipse  of  the  satellite,  as  stated  from 
calculation  in  tables,  is  the  instant  at  which  the  satellite  would  appear  to 
enter  or  emerge  from  the  shadow,  if  it  could  be  seen  by  an  observer  from 
the  sun,  S.  If  the  transmission  of  light  were  instantaneous,  it  is  obvious 
that  the  light  coming  from  Jupiter's  satellite,  E,  would  be  seen  at  the 
same  moment  at  the  points  T^  Sand  T'.  But  repeated  observation  shows 


244  SCIENCE   OF   COMMON   THINGS. 

How  a  multitude  of  persons  see  the  same  object.  Shadows. 

that  the  eclipse  takes  place  eight  minutes  earlier  than  the  calculated 
period  when  the  earth  is  in  the  nearest  point  of  its  orbit,  as  at  T,  and 
eight  minutes  later  when  she  is  in  the  opposite  part  of  her  orbit,  as  at  7", 
the  difference  in  the  distance  of  these  two  points  from  Jubiter  being 
190,000,000,  of  miles. 

1638  Why  can  a  thousand  persons  see  the  same  object  at  Hie  same 
time? 

Because  it  throws  off  from  its  surface  an  infinite 
number  of  rays  in  all  directions ;  and  one  person  sees 
one  portion  of  these  rays,  and  another  person  another. 

16J39    Why  can  we  not  see  the  stars  in  the  day-time  f 

Because  the  light  of  the  sun  is  so  powerful  that  it 
eclipses  the  feeble  light  of  the  stars ;  in  consequence 
of  whicli  they  are  invisible  by  day. 

1Q3O  In  what  manner  is  light  propagated  f 

In  right  lines  from  every  luminous  point,  every  such 
line  being  called  a  ray  of  light. 

1631   Wliat  do  we  mean  by  a  pencil  of 
light? 

A  collection  of  radiating  lines 
or  rays,  as  seen  in  Fig.  51. 

163S   What  is  darkness? 

The  absence  of  light. 

1633  What  is  a  shadow? 

A  shadow  is  the  name  given  to  the  comparative 
darkness  of  places  or  objects,  which  are  prevented  by 
intervening  things  from  receiving  the  direct  rays  of 
some  luminous  body  shining  on  the  objects  around. 

1634  Why  cannot  we  see  through  a  crooked  tube  as  well  as  through  a 
straight  one  ? 

Because  light  moves  only  in  straight  lines. 

1635  What  is  the  philosophy  of  taking  aim  with  a  gun  or  arrow  ? 

In  taking  aim  with  a  gun  or  arrow,  we  proceed  upon 
the  supposition  that  light  moves  in  straight  lines,  and 
try  to  make  the  projectile  go  to  the  desired  object  as 
nearly  as  possible  by  the  path  along  which  the  lig/it 
comes  from  the  object  to  the  eye. 

1636  Why  does  a  carpenter  look  along  the  edge  of  a  plank  to  see  if  it 
is  straight  ? 


SCIENCE   OF  COMMON  THINGS.  245 

Mirrors.  Reflection  of  light.  Incidence  and  reflection. 

If  the  edge  be  straight  and  uniform,  the  light  from 
all  points  of  the  edge  will  come  to  the  eye  regularly 
and  uniformly ;  if  irregularities,  however,  exist,  they 
will  cause  the  light  to  be  irregular,  and  the  eye  at 
once  notices  the  confusion  and  the  point  which  occa- 
sions it. 

37*   What  is  a  mirror  f 

Any  substance  reflecting  light.  The  term  is  gene- 
rally applied  to  glass  covered  on  the  back  with  quiet 
silver. 

1038  When  liglit  falls  upon  a  body,  in  what  three  ways  may  it  dispose 
of  itself? 

It  may  be  reflected,  refracted,  or  absorbed. 

1039  What  do  we  mean  when  we  speak  of  light  being  reflected? 

When  a  ray  of  light  strikes  against  a  surface,  and  is 
caused  to  turn  back  or  rebound  in  a  direction  different 
from  whence  it  proceeded,  it  is  said  to  be  reflected. 

1040  Why  do  we  see  ourselves  in  a  mirror  f 

Because  the  rays  of  light  from  our  face  strike  against 
the  glass,  and  (instead  or  being  transmitted)  are  reflect- 
ed, or  sent  back  again  to  our  eye. 

1041  Why  are  flie  rays  of  light  reflected  by  a  mirror  ? 

Because  they  cannot  pass  through  the  impenetrable 
metal  with  which  the  back  of  the  glass  is  covered  ;  so 
they  rebound  back,  just  as  a  marble  would  do  if  it  were 
thrown  against  a  wall. 

1043  When  a  marble  is  rotted  towards  a  waU,  what  is  the  path 
through  which  it  runs  called  ? 

The  line  of  incidence. 

1043  When  a  marbk,  rebounds  back  again,  what  is  the  path  it  then 
describes  called? 

The  line  of  reflection.  (See 
Fig.  52.) 

If  A  B  be  the  line  of  incidence, 
then  B  E  is  the  line  of  reflection; 
and  vice  versa. 

1044  When  the  light  of  our  face 
goes   to   the  glass,  what  is   the  path 

rough  which  it  goes  catted  ? 

11* 


246 


SCIENCE   OF   COMMON   THINGS. 


Lines  of  incidence  and  reflection.  Why  images  appear  inverted  in  water. 


The  line  of  incidence. 

1645  When  the  light  of  our  face  is  reflected  back  again  from  the  mir- 
ror, what  is  this  returning  path  called  f 

The  line  of  reflection. 

1646  What  is  the  angle  of  incidence  f 

The  angle  between  the  line  of  incidence  and  the  per- 
pendicular. 

1647  What  is  the  angle  of  reflection  ? 

The  angle  between  the  line  of  reflection  and  the  per- 
pendicular. (See  Fig.  52.) 

Let  F  B  C  (Fig.  53)  be  any  surface ;  D  B  a  perpendicular  to  it.  If  a 
marble  were  thrown  from  E  to  B,  and  bounded  back  to  A,  then  E  B  D 
would  be  the  angle  of  incidence,  and  DBA  the  angle  of  reflection. 

1648  Why  does  the  image  of  any  object  in  water  always  appear  in- 
verted f 

Because  the  angles  of  incidence  being  always  equal 
to  the  angles  of  reflection,  the  light  of  the  object,  reflect- 
ed to  our  eyes  from  the  surface  of  the  water,  comes  to 
us  with  the  same  direction  as  it  would  have  done,  had 
it  proceeded  directly  from  an  inverted  object  in  the 
water. 

In  Fig.  53,  the  light  proceeding  from  the  ar- 
row-head, A,  strikes  the  water  at  F,  and  is  re- 
flected to  G  and  that  from  the  barb,  B,  strikes 
the  water  at  E,  and  is  reflected  toG.  A  spec- 
tator standing  at  G  will  see  the  reflected 
lines,  E  G  and  F  G,  as  if  they  proceeded  di- 
rectly from  C  and  D.  Now  we  always  judge 
of  the  position  of  an  object  according  to  the 
direction  in  which  the  rays  of  light  repre- 
senting it  come  to  the  eye,  and  for  this 
reason  the  image  of  the  arrow,  A  B,  reflect- 
ed from  the  surface  of  water,  appears  to  be 
located  at  C  D.  It  is  also  plain  that  A  (the  more  elevated  object)  will 
strike  the  water,  and  be  projected  from  it  more  perpendicularly  than  the 
point  B ;  and  therefore  the  image  will  seem  inverted. 

164O  If  we  lay  a  looking-glass  upon  the  floor,  with  its  face  uppermost, 
and  place  a  candle  beside  it,  why  will  the  image  of  the  candle  seen  in  the 
mirror  by  a  person  standing  opposite  to  the  candle,  seem  as  much  below  the 
surface  of  the  glass  as  the  candle  itself  stands  above  the  glass  ? 

Because  the  incident  ray  coming  from  the  top  of  the 
candle,  strikes  the  surface  of  the  glass,  and  is  reflected 


Fig.  53. 


SCIENCE   OF   COMMON   THINGS.  247 


Why  the  image  in  a  mirror  seems  behind  the  glass. 


in  the  same  direction  that  a  ray  of  light  would  have 
taken,  had  it  really  come  from  a  candle  situated  as 
much  below  the  surface  of  the  glass,  as  the  first  candle 
was  above  the  surface.  This  fact  will  be  clearly  shown 
by  referring  to  Fig.  54. 


F,g.  54. 

165O  Why,  when  we  look  into  a  plane  mirror  (the  common  looking- 
glass)  does  our  image  appear  to  be  at  the  same  distance  behind  the  surface 
of  the  glass,  as  we  are  before  the  surface  f 

Because  the  lines  and  angles  of  incidence  being 
always  equal  to  the  lines  and  angles  of  reflection,  the 
rays  which  proceed  from  each  point  of  our  body 
before  the  mirror  will,  after  reflection,  proceed  as  if 
they  came  from  a  point  holding  a  corresponding  posi- 
tion behind  the  mirror ; — and  therefore  produce  the 
same  effect  upon  the  eye  of  an  observer  as  if  they 
actually  had  come  from 
that  point. 

For  this  reason  our  reflec- 
tion in  a  mirror  seems  to  ap- 
proach us  as  we  walk  towards 
it,  and  to  retire  from  us  as  we 
retire. 

The  whole  subject  of  the  re- 
flection of  images  being  gene- 
rally of  difficult  comprehen- 
sion by  most  persons,  Fig.  55 
is  introduced  as  a  means  of 
further  explanation. 

Let  A  be  a  part  of  an 
object  placed  before  a  looking- 
glass  M  N.  Let  A  B  and  A  C 
be  two  rays  diverging  from  it, 

and  refl  3cted  from  B  and  C  to     

an  eye  at  0,     After  reflexion     '  Fig  55, 


248  SCIENCE   OF   COMMON   THINGS. 

Peculiarities  of  reflected  light. 

they  will  proceed  as  if  they  had  issued  from  a  point  a  as  far  behind 
the  surface  of  the  looking-glass,  as  A  is  before  it — that  is  to  say,  the  dis- 
tance A  N  will  be  equal  to  the  distance  a  N.  In  seeing  an  object  with 
the  eye,  we  fix  upon  its  position  according  to  the  direction  in  which  the 
rays  of  light  coming  from  it  proceed,  and  do  not  take  into  account  the 
fact  that  the  rays  have  been  reflected  from  their  original  course. 

1651  Is  the  same  quantity  of  light  reflected  at  all  angles,  or  inclina- 
tions ? 

It  is  not :  when  the  angle  or  inclination  with  which  a 
ray  of  light  strikes  upon  a  reflecting  surface  is  great, 
the  amount  of  light  reflected  to  the  eye  will  be  con- 
siderable ;  when  the  angle,  or  inclination  is  small,  the 
amount  of  light  reflected  will  be  diminished 

1653  Why  does  a  spectator,  standing  upon  the  bank  of  a  river,  see  the 
images  of  the  opposite  bank,  and  objects  upon  it  reflected  in  the  water,  but 
not  the  images  of  any  near  object  ? 

Because  the  rays  of  light  coming  from  distant  objects 
strike  the  surface  of  the  water  very  obliquely,  and  the 
light  reflected  is  sufficient  to  make  a  sensible  impres- 
sion upon  the  eye,  while  the  light  proceeding  from 
near  objects  strikes  the  water  with  little  obliquity,  and 
the  light  reflected  is  not  sufficient  to  make  a  sensible 
impression  upon  the  eye. 

Tliis  fact  may  be  clearly  seen  by  reference  to  Fig.  56. 


Fig-  56. 

Let  S  be  the  position  of  the  spectator ;  O  and  B  the  position  of  distant 
objects.  The  rays  O  R  and  B  R  which  proceed  from  them,  strike  the 
surface  of  the  water  very  obliquely,  and  the  light  which  is  reflected  in 
the  direction  R  S  is  sufficient  to  make  a  sensible  impression  upon  the 
eye. 

But  in  regard  to  objects  such  as  A  placed  near  the  spectator,  they  are 
not  seen  reflected,  because  the  rays  A  R'  which  proceed  from  them  strike 
the  water  with  but  little  obliquity ;  and  consequently,  the  part  of  their 


SCIENCE   OF   COMMON   THINGS. 


240 


Why  windows  blaze  at  sunset. 


light  which  is  reflected  in  the  direction  R'  S,  towards  the  spectator,  is  not 
sufficient  to  produce  a  sensible  impression  upon  the  eye. 

1653    Why  do  windows  seem  to  blaze  at  sunrise  and  sunset  f 

Because  glass  is  a  good  reflector  of  light,  and  the 
rays  of  the  sun  (striking  against  the  window-glass)  are 
reflected,  or  thrown  back. 

1054  On  a  lake  of  water  the  moon  seems  to  make  a  path  of  light 
towards  the  eye  of  the  spectator,  while  ail  the  rest  of  the  lake  seems  dark  : 
why  is  this  ? 

The  reason  of  this  appearance  is  that  eveiy  little 
wave,  in  an  extent  perhaps  of  miles,  has  some  part  of 
its  rounded  surface  with  the  direction  or  obliquity 
which,  according  to  the  required  relation  of  the  angles 
of  incidence  and  reflection,  fits  it  to  reflect  the  light  to 
the  eye,  and  hence  every  wave  in  that  extent  sends  its 
momentary  gleam,  which  is  succeeded  by  others. 

1S55  In  a  sheet  of  water  at  noon,  the  sun  appears  to  shine  upon  only 
one  spot,  and  all  the  rest  of  the  water  seems  dark :  why  is  this  f 

Because  the  rays  fall 
at  various  degrees  of 
obliquity  on  the  water, 
and  are  reflected  at 
similar  angles  /  but  as 
only  those  which  meet 
the  eye  of  the  spectator 
are  visible,  all  the  water 
will  appear  dark  ex- 
cept that  one  spot. 

Here,  of  the  rays  S  A,  S  B, 
and  S  C,  only  the  ray  S  C 
meets  the  eye  of  the  specta- 
tor D.  The  spot  C,  therefore, 
will  appear  luminous  to  the 
spectator  D,  but  no  other  spot  of  the  water  ABC. 

1050  Why  can  we  not  see  into  the  street  or  road  when  candle*  are 
lighted  f 

1.  Because  glass  is  a  reflector,  and  throws  the  candle- 
light lack  into  the  room  again ;  and 

2.  The  pupil  of  the  eye  (having  become  contracted 
by  the  light  of  the  room)  is  too  small  to  collect  rays 


Fig.  67 


250 


SCIENCE   OF   COMMON   THINGS. 


When  are  shadows  large,  and  when  small  ? 


enough  from  the    dark    street    to   enable   us   to  see 
into  ^t. 

1657  Why  do  we  often  see  the  fire  reflected  in  our  windows  in  winter- 
time f 

Because  glass  is  a  good  reflector,  and  the  rays  of  the 
fire  (striking  against  the  window-glass)  are  reflected 
back  into  the  room  again. 

1058  If  the  shadow  of  an  object  be  thrown  on  a  wall,  the  closer  the  object 

is  held  to  the  candle,  the  larger 
,.---|I      will  be  its  shadow :  why  is  thisf 

,,/"''  Because  the  rays  of 

light  diverge  (from  the 
flame  of  a  candle)  in 
straight  lines,  like  lines 
drawn  from  the  centre 
of  a  circle. 

Here  the  arrow  A,  held  close 
to    the  candle,    will  cast  the 
shadow  B  F  on  a  wall ;  while 
~^\,  V       the  same    arrow,    held  at  C, 
"x»       would  cast  only  the  little  sha- 

*.*  dowDE- 

1659  How  do  we  judge  of  the  position,  distance,  and  size  of  an  object  f 

We  judge  of  the  position  and  distance  and  size  of  an 
object  by  the  relative  direction  of  lines  drawn  from  the 
object  to  the  eye,  and  by  the  angle  which  the  intersec- 
tion of  these  lines  makes  with  the  eye.  This  angle  is 
called  the  angle  of  vision. 


"""•—  > 

"~ti 


Fig,  50. 

The  student  will  bear  in  mind  that  an  angle  is  simply  the  inclination 
of  two  lines  without  any  regard  to  their  length.  Thus,  in  Fig.  59,  the 
inclination  of  the  lines,  caused  by  rays  of  light  proceeding  from  A  and  B, 


SCIENCE   OF   COMMON   THINGS.  251 

How  we  estimaUthe  size  and  position  of  distant  objects. 

and  from  C  and  7>,  and  meeting  at  the  eye,  forms  an  angle  at  the  point 
of  intersection,  which  is  the  eye.  This  angle  is  the  angle  of  vision.  As 
the  inclination  of  the  ines  proceeding  from  A  and  B,  and  from  C  and  Z>, 
is  the  same,  the  angles  will  be  equal,  and  the  man  and  the  bird  will  ap- 
pear of  the  same  size. 

1660  Why  does  a  man  on  the  top  of  a  mountain  or  church-spire  seem 
ti  be  no  larger  than  a  crow  t 

Because  the  angle  made  in  our  eye  by  the  perpen- 
dicular height  of  the  man  at  that  distance  is  no  larger 
than  that  made  by  a  crow  close  by. 

Let  A  B  (Fig.  59)  be  a  man  on  a  distant  mountain  or  spire,  and  C  I)  A 
crow  close  by,  the  man  will  appear  only  as  high  as  the  line  C  D,  which 
is  the  height  of  the  crow.  For  the  same  reason  the  trees  and  houses  far 
down  a  street  or  avenue  appear  smaller  than  those  near  by. 

1661  Why  does  the  moon  appear  to  us  so  much  larger  than  the  stars, 
though,  in  fact,  it  is  a  great  deal  smaller  ? 

Because  the  moon  is  very  much  nearer  to  us  than  any 
of  the  stars. 


Fig.  60. 

Let  A  B  represent  a  fixed  star,  and  C  D  the  moon.  The  angle  of 
vision,  A  G  B,  which  the  fixed  star,  A  B,  makes  with  the  eye  is  evidently 
less  than  the  angle  of  vision,  G  G  D,  which  the  moon  makes  with  the  eye. 
But  we  judge  of  the  size  of  a  body  by  the  size  of  the  angle,  and  therefore 
the  moon,  which  is  nearest  and  makes  the  greatest  angle  of  vision,  ap- 
pears the  largest.  A  B,  though  much  the  larger  body,  will  appear  no 
bigger  than  E F;  whereas  the  moon  (CD)  will  appear  as  large  as  the 
line,  0  D,  to  the  spectator,  G. 

The  moon  is  240,000  miles  from  the  earth,  not  quite  a  quarter  of  a 
million  of  miles.  The  nearest  fixed  stars  are  20,000,000,000,000  (that  is, 
twenty  billions). 

1663  Why  does  the  moon  (which  is  a  sphere)  appear  to  be  a  fiat  sur- 
face f 

Because  it  is  so  far  off  that  we  cannot  distinguish  any 
difference  between  the  length  of  the  rays  issuing  from 
'the  edge  and  those  which  issue  from  the  centre. 


253  SCIENCE   OF   COMMON   THINGS. 


Why  objects  in  the  shade  seem  dark,  t        Telescopes. 

The  rays  A  D  and  C  D 
appear  to  be  no  longer 
than  the  ray  B  1) ;  but  if 
all  the  rays  seem  of  the 
same  length,  the  part  B 
will  not  seem  to  be  nearer 
to  us  than  A  and  C ' ;  and  therefore  ABO  will  look  like  a  flat  or  straight 
line.  The  rays  A  D  and  C  D  are  240,000  miles  long.  The  ray  B  D  is 
238,910  miles  long. 

1603  An  object  in  the  shade  is  not  so  bright  and  apparent  as  an  object 
in  the  sun :  why  is  it  not  f 

Because  objects  in  the  shade  are  seen  by  reflected 
light  reflected ;  that  is,  the  light  is  twice  reflected ; 
and,  as  the  rays  of  light  are  always  absorbed  in  some 
measure  by  every  substance  on  which  they  fall,  and 
also  scattered  by  irregular  reflections,  therefore  in  the 
two  reflections  much  light  is  lost,  and  the  object  is  seen 
with  less  distinctness. 

Part  of  the  rays  are  absorbed,  and  part  are  scattered  in  all  directions 
by  irregular  reflections ;  so  that  rarely  more  than  half  are  reflected,  even 
from  the  most  polished  metals. 

1664  Why  is  it  light  when  the  sky  is  covered  with  thick  clouds  ? 

Partially  because  the  sun's  light  is  transmitted 
through  the  clouds,  and  partially  on  account  of  the 
multiplied  reflections  of  light  in  the  atmosphere. 

1665  What  is  the  use  of  telescopes  f 

They  gather  together  the  rays  of  light,  and  a  greater 
number  are  thus  brought  to  the  eye. 

1666  How  can  these  rays  be  gathered  together  ? 

Rays  of  light  diverge — that  is,  spread  out  in  all  direc- 
tions— from  a  luminous  object.  The  number  of  these 
diverging  rays  which  will  enter  the  eye  is  limited  by 
the  size  of  the  pupil.  But  before  they  reach  the  eye, 
they  may  be  received  upon  a  glass  lens  of  a  convex 
form,  which  will  have  the  effect  of  collecting  them  into 
a  space  less  in  magnitude  than  the  pupil  of  the  eye.  If 
the  eye  be  placed  where  the  rays  are  thus  collected,  all 
the  light  will  enter  the  pupil. 

The  light  which  produces  vision,  as  will  be  more  fully  explained  here- 
after, enters  the  eye  through  a  circular  opening  called  the  pupil,  which  is 
the  black  circular  spot  surrounded  by  a  colored  ring,  appearing  in  the 


SCIENCE   OF  COMMON  THINGS. 


253 


How  telescopes  assist  the  sight. 


Fig.  62. 


FiK.es. 

centre  of  the  front  of  the  eye.  Noy,  as  the  rays  of  light  proceeding  from 
an  object  diverge,  or  spread  out,  the  number  which  will  enter  the  eye  will 
be  limited  by  the  size  of  the  pupil.  At  a  great  distance  from  an  object, 
as  will  be  seen  in  Fig.  62,  few  rays  will  enter  the  eye ;  but  if,  as  in  Fig. 
63,  we  place  before  the  eye  a  piece  of  glass,  called  a  lens,  so  constructed 
as  to  collect  all  the  diverging  rays  together,  the  light  will  be  concentrated 
at  one  point,  and  in  sufficient  quantity  to  enable  us  to  see  distinctly. 

1607  Why  do  telescopes  enable  us  to  see  objects  invisible  to  the  naked 
eyef 

Because  they  gather  together  more  luminous  rays 
from  obscure  objects  than  the  eye  can,  and  form  a  bright 
image  of  them  m  the  tube  of  the  telescope,  where  by 
means  of  lenses  they  are  magnified. 

1608  When  a  ship  (out  at  sea)  is  approaching  the  shore,  why  do  we 
see  the  small  masts  before  we  see  the  bulky  hull  ? 

Because  the  earth  is  round;  and  the  curve  of  the  sea 
hides  the  hull  from  our  eyes  after  the  tall  moists  have 
become  visible. 


Fig  64. 

Here  only  that  part  of  the  ship  above  the  line  A  C  can  be  seen  by  the 
gpectator,  A ;  the  rest  of  the  ship  is  hidden  by  the  swell  of  the  curve  D  E. 

The  diminution  of  the  size  of  a  ship  seen  at  sea,  owing  to  the  convexity 
of  the  earth  and  the  distance  of  the  observer,  is  also  illustrated  in  Fig.  65k, 

1669    What  is  meant  by  the  rejraction  of  light? 

Light  traverses  a  given  transparent  substance,  such  as 


254: 


SCIENCE  OF   COMMON   THINGS. 


Refraction  of  light. 


A  stick  partially  in  water  seems  broken. 


Fig.  66- 


Fig  65. 

air,  water,  or  glass,  in  a  straight  line,  provided  no 
reflection  occurs  and  there  is  no  change  of  density  in 
the  composition  of  the  medium ;  but  when  light  passes 
from  one  medium  into  another,  or  from  one  part  of  the 
same  medium  into  another  part  of  a  different  density, 
it  is  lent  from  a  straight  line,  or  refracted. 

In  Fig.  66,  suppose  n  m  to  represent  the  sur- 
face of  water,  and  S  0  a  ray  of  light  striking 
upon  its  surface.  When  this  ray  S  O  enters 
the  water,  it  will  no  longer  pursue  a  straight 
course,  but  will  be  refracted,  or  bent  towards 
the  perpendicular  line,  A  B,  as  in  the  case  of  S  0 
H.  The  denser  the  water,  or  other  fluid,  may 
be,  the  more  the  ray  S  O  H  will  be  refracted,  or 
turned  towards  A  B. 
167O  Does  air  possess  the  property  of  refracting  light  f 

Yes ;  the  more  dense  the  air,  the  greater  is  its  refrac- 
tive power. 

167f  1   Why  does  the  part  of  a  stick  immersed  in  the  water  appear  lent 
or  broken  ? 

The  water  and  the  air  being  of  different  densities, 
the  rays  of  light  proceeding  from  the  part  of  the  stick 
contained  in  the  water  are  refracted,  or  caused  to  deviate 
from  a  straight  line  as  they  pass  from  the  water  into 
i  the  air ;  consequently  that  portion  of  the 
[stick  immersed  in  the  water  will  appear 
to  be  lifted  up,  or  to  be  lent  in  such  a 
manner  as  to  form  an  angle  with  the  part 
|  out  of  the  water. 

The  bent  appearance  of  the  stick  in  water  is  repre- 
||  sented  in  Fig.  67.     For  the  same  reason,  a  spoon  in  a 
glass  of  water,  or  an  oar  partially  immersed  in  water, 
always  appears  beut. 


SCIENCE   OF  COMMON   THINGS.  255 

Rivera  deeper  than  they  appear  to  be.  Compound  nature  of  white  light. 

167*8   Why  does  a  river  always  appear  more  shallow  than  it  really  is  1 

Because  the  light  proceeding  from  the  bottom  of  the 
river  is  refracted  as  it  emerges  out  of  the  water,  and 
causes  the  bottom  to  appear  elevated. 

167*3  How  much  deeper  is  a  river  than  it  seems  to  be? 

About  one-third.  If,  therefore,  a  river  seems  only 
four  feet  deep,  it  is  really  six  feet  deep. 

Many  persons  get  out  of  their  depth  in  bathing  in  consequence  of  this 
deception. 

The  following  simple  experi- 
ment illustrates  the  effect  of  re- 
fraction:— Place  a  silver  coin,  i 
m,  at  the  bottom  of  a  basin,  Fig. 
68.  The  rays,  i  *,  proceeding  to 
the  eye  from  the  silver  surface, 
render  the  coin  visible.  The 
point  a,  the  eye,  is  then  moved 
farther  back,  so  that  the  edge  of 
the  basin  obstructs  the  direct 
rays,  and  of  course  the  coin  is 
no  longer  seen.  If  an  attendant 
carefully  pours  water  into  the 
basin,  so  that  the  object  is  not  moved,  it  will  presently,  as  the  water  rises 
in  the  basin,  become  again  visible.  This  arises  from  the  refraction  of  the 
rays  by  the  water,  the  image,  indeed,  appearing  at  n  instead  of  at  m. 

167*4  Is  a  ray  of  white  light  simple  or  compound? 

Every  ray  of  white  light  is  compounded  of  other  rays 
of  colored  light. 

1675  Into  how  many  parts  may  a  ray  of  light  be  divided  f 

Into  three  parts  :  blue,  yellow,  and  red. 

These  three  colors,  by  combination,  make  seven :  1,  red ;  2,  orange  (or 
red  and  yellow) ;  3,  yettow ;  4,  green  (or  yellow  and  blue) ;  5,  blue ;  6,  in- 
digo (a  shade  of  blue) ;  and,  7,  viokt  (or  blue  and  red). 

1676  How  is  it  known  that  a  ray  of  light  consists  of  several  different 
colors  f 

Because  if  a  ray  of  light  be  cast  upon  a  triangular 
piece  of  glass  (called  a  prism),  it  will  be  distinctly 
divided  into  seven  colors :  1,  red ;  2,  orange ;  3,  yel- 
low ;  4,  green ;  5,  blue  ;  6,  indigo ;  and,  7,  violet. 

1677  Why  does  a  prism  divide  a  ray  of  light  into  various  colors  f 

Because  all  these  colors  are  refracted,  or  bent  out  of 
their  course  differently.  Red  is  refracted  least,  and 
blue  the  most ;  therefore,  the  blue  ray  will  be  bent  to 


256  SCIENCE   OF   COMMON   THINGS. 

Effects  of  a  prism  In  separating  the  rays  of  light. 

the  top  of  the  prism,  and  the  red  will  remain  at  the 
bottom. 


Violet 

Indigo. 

Blue? 

Green. 

Yellow. 

Orange. 

Ked. 


Fig.  by. 

This  separation  of  a  ray  of  solar  light  into  different  colors,  by  refraction, 
is  represented  in  Fig.  69.  A  ray  of  light,  £  A,  is  admitted  through  an 
aperture  in  a  window-shutter  into  a  darkened  chamber,  and  caused  to  fall 
on  a  prism,  P.  The  ray  thus  entering  would,  if  allowed  to  pass  unob- 
structedly,  have  moved  in  a  straight  line  to  the  point  K,  on  the  floor  of 
the  room ;  but  the  prism  being  so  placed  that  the  ray  may  enter  and  quit 
it  at  equal  angles,  it  will  be  refracted  in  such  a  manner  as  to  form  on  the 
opposite  side  of  the  room  an  oblong  image  called  the  solar  spectrum, 
divided  horizontally  into  seven  colored  spaces  or  bands  of  unequal  extent, 
succeeding  each  other  in  the  order  represented:  red,  orange,  yellow,  green, 
blue,  indigo,  viokt. 

1678  Are  the  colored  rays,  once  separated  and  refracted  from  the 
prism,  capable  of  being  analyzed  by  refraction  again  ? 

They  are  not,  and  are  hence  designated  as  primary 
colors. 

1679  If  the  seven  different  colors  as  separated  by  the  prism  be  again 
collected  together,  what  will  they  form  ? 

White  light. 

1G8O  To  what  is  the  great  brilliancy  of  the  diamond  and  other  precious 
stones  due  ? 

To  their  power  of  refracting  light ;  they  are  also 
artificially  cut  in  such  a  manner  as  to  form  a  series  of 
prisms,,  which  separate  the  rays  of  light  falling  on 
mem  into  their  component  colored  rays. 

1GS1    What  is  a  rainbow  f 

The  rainbow  is  a  semicircular  l>and  or  arc,  composed 


SCIENCE    OF   COMMON   THINGS. 


257 


Production  and  explanation  of  the  rainbow 


of  the  different  colors,  generally  exhibited  upon  the 
clouds  during  the  occurrence  of  rain  in  sunshine. 

If  we  take  a  glass  globe  filled  with  water,  and  suspend  it  at  a  certain 
height  in  the  solar  rays  above  the  eye,  a  spectator  standing  with  his  back 
to  the  sun  will  see  the  refraction  and  reflection  of  red  light ;  if,  then,  the 
globe  be  lowered  slowly,  the  observer  retaining  his  position,  the  red  light 
will  be  replaced  by  orange,  and  this  in  its  turn  by  yellow,  and  so  on,  the 
globe  at  different  heights  presenting  to  the  eye  the  seven  primitive  colors 
iri  succession.  If  now,  in  the  place  of  the  globe  occupying  different  posi- 
tions, we  substitute  drops  of  water,  we  have  a  ready  explanation  of  the 
phenomena  of  the  rainbow. 


Fig  70. 


Let  -A,  B,  and  C  be  three  drops  of  rain ;  S  A,  S  B,  and  S  C,  three  rays 
of  the  sun.  £  A  is  divided  into  three  colors ;  the  blue  and  yellow  are 
bent  above  the  eye,  D,  and  the  red  enters  it. 

The  ray,  S  B,  is  divided  into  three  colors ;  the  blue  is  bent  above  the 
eye,  and  the  red  falls  below  the  eye,  D,  but  the  yellow  enters  it. 

The  ray,  S  C,  is  also  divided  into  the  three  colors.  The  blue  (which  is 
bent  most)  enters  the  eye ;  and  the  other  two  fall  below  it.  Thus  the 
eye  sees  the  blue  of  (7,  and  of  all  drops  in  the  position  of  C;  the  yellow 
of  B,  and  of  all  drops  in  the  position  of  B ;  and  the  red  of  A,  and  of  all 
drops  in  the  position  of  A  ;  and  thus  it  sees  a  rainbow. 

1683   What  is  the  occasion  of  the  rainbow  f 

The  rainbow  is  produced  by  the  refraction  ana  re- 
flection of  the  solar  rays  in  the  drops  oi  falling  rain. 

1683  What  are  the  conditions  necessary  in  order  that  we  may  see  a 
rainbow  f 

The  rainbow  can  be  seen  only  when  it  rains,  and  in 
that  point  of  the  heavens  which  is  opposite  to  the  sun. 
It  is  necessary  also  that  the  sun  should  not  have  too 


258 


SCIENCE   OF   COMMON   THINGS. 


No  two  persons  see  the  same  rainbow.    Formation  of  two  rainbows  at  the  same  time 

great  an  altitude  above  the  horizon.  Hence,  within  a 
certain  interval  each  day,  no  visible  rainbows  can  be 
formed,  on  account  of  the  sun's  high  altitude  above  the 
horizon. 

1684  How  do  we  know  that  the  rainbow  results  from  the  decomposition 
of  the  solar  rays  by  drops  of  water  1 

Because  in  the  case  of  cascades  and  water-falls,  the 
\spray  and  the  drops  of  moisture  dispersed  over  the 
igrass  and  the  spiders  -webs  produce  the  same  phenomena. 

1635  Does  every  person  see  the  same  colors  from  the  same  drops? 

No  ;  no  two  persons  see  the  same  rainbow. 

To  another  spectator,  the  rays  from  S  B  (Fig.  70)  might  be  red  instead 
of  yellow ;  the  ray  from  S  C,  yellow ;  and  the  blue  might  be  reflected 
from  some  drop  below  C.  To  a  third  person,  the  red  may  issue  from  a 
drop  above  A,  and  then  A  would  reflect  the  yellow,  and  B  the  blue,  and 
so  on. 

1686   Why  are  there  often  two  rainbows  at  one  and  the  same  time  f 

The  first,  or  primary  bow,  is  formed  by  two  refrac- 
tions of  the  solar  ray,  and  one  reflection,  tne  rays  of  the 
sun  entering  the  drops  at  the  top,  and  being  reflected 
to  the  eye  from  the  bottom. 

Thus  in  Fig.  71,  the  ray  S  A  of  the 
primary  rainbow  strikes  the  drop  at  A, 
is  refracted  or  bent  to  B,  the  back  part 
of  the  inner  surface  of  the  drop  ;  it  is 
then  refracted  to  C,  the  lower  part  of 
the  drop,  when  it  is  refracted  again, 
and  so  bent  as  to  come  directly  to  the 
eye  of  the  spectator. 

The  secondary,  or  outer  bow,  is  pro- 
duced, on  the  contrary,  by  two  refrac- 
tions and  two  reflections,  the  ray  of 
light  entering  the  drops  from  the  bot- 
tom, and  being  reflected  to  the  eye 
from  the  top. 

Thus  in  Fig.  72,  the  ray  S  B  of  the 
secondary  bow  strikes  the  bottom  of 
the  drop  at  B,  is  refracted  to  A,  is  then 
reflected  to  C,  is  again  reflected  to  D, 
when  it  is  again  refracted  or  bent,  till 
it  reaches  the  eye  of  the  spectator. 

1687  Why  are  the  colors  of  the 
second  bow  all  reversed  1 

jne.  re.  Because  in  one  bow  we  sea 


SCIENCE   OF   COMMON   THINGS.  259 

Colors  in  a  soap-bubble.  Origin  of  morning  and  evening  twilight. 

the  rays   which  enter  at  the   top  of  the   rain-drops, 
refracted  from  the  bottom  : 

But  in  the  other  bow  we  see  the  rays  which  enter  at 
the  bottom  of  the  rain-drops  (after  two  reflections) 
refracted  from  the  top. 

The  position  and  formation  of  the  primary  and  secondary  rainbows  are 
represented  in  Fig.  73.  Thus  in  the  formation  of  the  primary  bow,  the 
ray  of  light  S  strikes  the  drop  n  at  a,  is  refracted  to  n  &,  thence  to  g,  and 
leaving  the  drop  at  this  point,  proceeds  to  the  eyes  of  the  spectator  at  0. 
In  the  formation  of  the  secondary  bow,  the  ray  S'  strikes  the  drop  p  at  the 
bottom  at  the  point  i,  is  refracted  to  rf,  thence  to/,  and  again  to  e,  pro- 
ceeding from  the  top  of  the  drop,  also  to  the  eye  of  the  spectator  at  0. 

The  reason  why  the  primary  bow  exhibits  the  stronger  colors  is,  be- 
cause the  colors  are  seen  after  one  reflection  and  two  refractions ;  but  the 
colors  of  the  secondary  (or  upper)  rainbow  undergo  two  reflections  and 
two  refractions. 


Fig.  73. 

1688   Why  does  a  soap  bubble  exhibit  such  a  variety  of  colors  f 
Because  the  thickness  of  the  film  through  which  the 
rays  pass  is  constantly  varying. 

1680    Why  is  a  soap  bubble  so  constantly  changing  its  thickness  t 

Because  the  water  runs  down  from  the  top  to  the 
bottom  of  the  bubble,  till  the  crown  becomes  so  thin  as 
to  burst. 

3  60O    Wliat  is  the  cause  of  morning  and  evening  twilight  f 

When  the  sun  is  below  the  horizon,  the  rays  which 
strike  upon  the  atmosphere  or  clouds  are  bent  down 


260 


SCIENCE   OF   COMMON   THINGS. 


Lenses  and  their  varieties. 


What  is  a  focus  of  light? 


towards  the  earth,  and  produce  a  little  light  called  twi- 
light. 

1691    What  is  a  lens  f 

A  piece  of  glass  or  other  transparent  substance, 
bounded  on  both  sides  by  polished  spherical  surfaces, 
or  on  the  one  side  by  a  spherical,  and  on  the  other  by  a 
plane  surface.  Rays  of  light  passing  through  it  are 
made  to  change  their  direction,  and  to  magnify  or 
diminish  the  appearance  of  objects  at  a  certain  distance. 

1603  Sow  many  varieties  of  lenses  are  generally  recognised  f 

Two  :  convex  and  concave. 


Fij?.  74. 

Among  convex  lenses  are  the  double  convex  A  (Fig.  74)  to  which  the 
appellation  lens  was  originally  applied  from  its  resemblance  to  a  lentil- 
seed  (kns  in  Latin)  being  bounded  by  two  convex  spherical  surfaces 
whose  centres  are  on  opposite  sides  of  the  lens ;  the  plano-convex  B, 
having  one  side  bounded  by  a  plane  surface,  and  the  other  by  a  convex 
surface ;  and  the  meniscus  or  concavo-convex  C,  bounded  on  one  side  by 
a  concave,  and  on  the  other  by  a  convex  surface. 

There  are  also  three  principal  varieties  of  concave  glasses;  as  the 
double  concave  D,  bounded  by  two  concave  surfaces,  forming  portions  of 
spheres  whose  centres  are  on  opposite  sides  of  the  lens;  the  plano- 
concave E,  bounded  on  one  side  by  a  plane,  and  on  the  other  by  a 
concave  surface ;  and  convexo-concave  F,  bounded  by  a  convex  surface 
on  one  side,  and  by  a  concave  one  on  the  other. 

1693    What  is  a  focus  of  light  f 

"When  rays  of  light  continually  approach  each  other, 
as  in  moving  to  a  point,  they  are  said  to  converge,  and 
the  point  at  which  the  converging  rays  meet  is  called 
tliejocus. 

1694   What  sort  of  a  lens  is  a  common  burn- 
ing-glass ? 

A  double  convex  lens. 

Fig.  75  represents  the  action  of  a  double  con- 
vex lens  in  causing  the  rays  of  light  to  converge 
and  meet  at  a  focus. 
Figi  75.  1695    What  are  transparent  bodies  f 


SCIENCE   OF   COMMON   THINGS.  261 

Opaque  and  transparent  bodies.  Absorption  of  light. 

Those  which  do  not  irvterrupt  the ,  passage  of  light, 
or  which  admit  of  other  bodies  being  seen  through 
them. 

1606  When  is  a  body  said  io  be  opaque  ? 

When  it  entirely  prevents  the  passage  of  light. 

1607  Is  there  any  body  perfectly  transparent  f 

No ;  some  light  is  evidently  lost  in  passing  even 
through  space,  and  still  more  in  traversing  our  atmo- 
sphere. 

160S  Row  much  of  Vie  sun's  light  is  supposed  to  be  intercepted  by  the 

atmosphere  ? 

It  has  been  calculated  that  the  atmosphere,  when  the 
rajs  of  the  sun  ^>ass  perpendicularly  through  it,  inter- 
cepts from  one-fifth  to  one-fourth  of  their  light;  but 
when  the  sun  is  near  the  horizon,  and  the  mass  of  air 
through  which  the  solar  rays  pass  is  consequently 
vastly  increased  in  thickness,  only  one  two  hundred  and 
twelfth  part  of  their  light  can  reach  the  surface  of  the 
earth. 

1S00    Why  is  charcoal  black  f 

Because  it  absorbs  all  the  light  which  falls  upon  it, 
and  reflects  none. 

1*700    What  becomes  of  the  light  which  is  absorbed? 

This  question  cannot  be  satisfactorily  answered.  In 
all  probability  it  is  permanently  retained  within  the 
substance  of  the  absorbing  body. 

1*7O1   To  what  depth  is  light  supposed  to  penetrate  tJie  ocean  f 

It  is  calculated  that  sea  water  loses  all  its  transpa- 
rency at  the  depth  of  seven  hundred  and  thirty  feet ; 
but  a  dim  twilight  must  prevail  much  deeper  in  the 
ocean. 

12 


262  SCIENCE    OF   COMMON   THINGS. 

Structure  of  the  eye.  How  the  eye  is  moved. 

CHAPTER    II. 

STRUCTURE   OF   THE   EYE   AND   THE   PHENOMENA   OF  VISION. 
1*703    What  is  the  structure  of  the  human  eye  ? 

In  man  the  organ  of  vision  consists  of  two  hollow 
spheres,  each  about  an  inch  in  diameter,  filled  with 
certain  transparent  liquids,  and  deposited  in  cavities  of 
suitable  magnitude  and  form  in  the  upper  part  of  the 
front  of  the  head  on  each  side  the  nose. 

±7O3  How  is  it  that  we  are  enabled  to  move  the  eye  in  various  directions  t 

By  means  of  muscles  attached  to  different  points  of 
its  surface. 


These  are  shown  in  Fig.  76.  where  the  external  bones  of  the  temple 
are  supposed  to  be  removed  in  order  to  render  visible  the  muscular 
arrangements.  The  muscle,  1,  raises  the  eye-lid,  and  is  constantly  in 
action  while  we  are  awake.  During  sleep,  the  muscle  being  in  repose 
and  relaxed,  the  eye-lid  falls  and  protects  the  eye  from  the  action  of  light. 
The  muscle,  4,  turns  the  eye  upwards ;  5,  downwards ;  6,  outwards ;  and 
a  corresponding  one  on  the  inside,  not  seen  in  the  figure,  turns  it  inwards. 
No.  2  and  10  turn  the  eye  round  its  axis.  No.  11  is  tue  great  optic 


SCIENCE   OF   COMMON   THINGS.  263 

Eetina.  Iris.  Pupil.  Cornea 

nerve,  which  conveys  the  sensation  to  the  brain.  If  this  nerve  were  cut, 
notwithstanding  the  eye  might  be  in  other  respects  perfect,  the  sense  of 
sight  would  be  destroyed. 

1704  Of  what  parts  does  the  eye  consist  f 

The  eye  is  of  globular  form,  and  is  composed  of  three 
coats  or  membranes,  called  the  sclerotic,  the  choroid, 
and  the  retina;  and  three  humors,  denominated  the 
aqueous  ',  the  crystalline,  and  the  vitreous. 

1705  What  is  meant  by  the  "  retina  of  the  eye  ?" 

The  network  which  lines  the  back  of  the  eye  is  called 
the  retina  ;  it  is  composed  of  an  expansion  of  the  optic 
nerve. 

1706  What  is  that  portion  of  the  eye  called  ivhich  in  some  persons  is 
blue,  in  others  gray  or  hazel  ? 

It  is  called  the  iris. 

17*O  7*  In  the  centre  of  the  iris  is  a  circular  "black  opening  :  what  is  this 
called  1 

It  is  called  the  pupil.  But  this  spot  is  not  a  black 
substance,  but  an  aperture,  which  appears  black  only 
because  the  chamber  within  it  is  dark.  It  is  properly 
speaking  the  window  of  the  eye,  through  which  light 
is  admitted,  which  strikes  on  the  retina. 

17*O8  Does  light  admitted  through  the  pupil  to  the  retina  produce  vision  ? 

Yes,  provided  the  light  enter  in  sufficient  quantity. 


How  by  the  arrangement  of  the  several  parts  of  the  eye  are  we 
enabled  to  see? 

The  rays  of  light  falling  upon  the  cornea,  enter  the 
interior  of  the  eye  through  the  pupil,  and  by  the  joint 
action  of  the  cornea  and  crystalline  lens  are  brought  to 
a  focus  at  the  back  part  of  the  eve,  upon  the  retina. 
Here  an  image  is  formed,  and  the  impression  it  makes 
is  conveyed  along  the  optic  nerve  to  the  brain. 

17*1O   What  is  meant  "by  Hie  "  cornea  of  the  eye  ?" 

All  the  outside  of  the  visible  part  of  the  eyeball. 

Fig.  77  represents  the  interior  construction  of  the  eye.  It  is  composed, 
in  the  first  place,  of  the  cornea,  a,  a  transparent  membrane  in  front  of  the 
globe  of  the  eye.  Next  is  the  sclerotic  coat,  t,  which  joins  on  the  cornea, 
and  upon  which  the  external  form  of  the  eye  depends.  The  cornea  is 
united  to,  or  fixed  in,  the  sclerotic  coat,  like  the  glass  into  the  case  of  a 
watch  :  d,  c  represents  the  iris,  with  an  opening  in  it,  forming  the  pupil 


SCIENCE   OF   COMMON   THINGS. 


Explanation  of  near-sightedness. 


Next  in  order  is  the  aqueous  humor,  &,  e,  in  the  middle  of  which  is  the 
iris,  d,  c.  Behind  the  pupil  we  have  the  crystalline. lens, /,  and  then  the 
vitreous  humor,  A,  filling  all  the  interior  of  the  ball  of  the  eye.  m  indi- 
cates the  retina,  which  is  an  expansion  of  the  optic  nerve,  n.  k  is  the 
choroid  coat,  a  membrane  interposed  between  the  retina  and  the  sclerotic 
coat ;  it  terminates  in  form  in  a  series  of  folds  or  filaments,  #,  called  the 
ciliary  ligament  or  processes. 

1711    Why  are  some  persons  near-sighted  ? 

Because  the  curvature  of  the  cornea  and  the  crystal- 
line lens  is  too  great,  and  the  rays  of  light  which  form 
the  image  are  brought  to  a  focus  before  they  reach  the 
retina  or  the  back  part  of  the  eye.  The  object,  there- 
fore, is  not  distinctly  seen. 

Fig.  79  represents  the  manner 
in  which  the  image  is  formed 
upon  the  retina  in  the  perfect  eye. 
The  curvature  of  the  cornea,  s  s, 
and  of  the  crystalline  lens,  c  c,  is 
just  sufficient  to  cause  the  rays 
of  light  proceeding  from  the  im- 
age, e  e,  to  converge  to  the  right 
focus,  m,  upon  the  retina. 

Fig.  78  represents  the  man- 
ner in  which  the  image  is  formed 
in  the  eye  of  a  near-sighted  per- 
son. The  curvature  of  the  cor- 
nea, s  5,  and  of  the  crystalline 
lens,  c  c,  is  so  great  that  the  im- 
age is  formed  at  m  m  in  advance 
of  the  retina. 


SCIENCE   OF   COMMON   THINGS. 


Explanation  of  far-sightedness. 


What  sort  of  glasses  do  near-sighted  persons  wear  ? 

If  the  cornea  and  crystalline  lens  be  too  convex  (or 
projecting),  the  person  must  wear  double  concave  glasses 
to  counteract  it. 

17*13    What  is  meant  by  "  double  concave  glasses  ?" 

Glasses  hollowed-in  on  both  sides. 

1  714    Why  are  old  people  far-sighted  ? 

<  Because  the  humors  of  their  eves  are  dried  up  by  age; 
in  consequence  of  which  the  cornea  sinks  in,  or  becomes 
flattened. 

17*15  Why  does  the  flattening  of  the  cornea  prevent  persons  seeing 
objects  which  are  near  ? 

Because  the  cornea  is  too  flat,  and  the  image  of  ob- 
jects is  not  completely  formed  when  their  rays  reach  the 
retina  /  in  consequence  of  which  the  image  is  imper- 
fect and  confused. 

Fig.  80  represents  the  man- 
ner in  which  the  image  is 
formed  in  the  eye,  when  the 
cornea  or  crystalline  lens  is 
flattened.  The  perfect  image 
would  be  produced  at  m  m, 
behind  the  retina,  and,  of 

course,  beyond  the  point  ne-  FJ    ^ 

cessary  to  secure  perfect  vision. 

17*16   What  sort  of  spectacle-glasses  are  suitable  for  old  people  f 

Double-convex  glasses,  or  those  which  curve  outwards 
on  both  sides.  These  shorten  the  focus  of  the  eye,  and 
produce  an  image  upon  the  right  point,  the  retina. 

1717*  Why  do  near-sighted  persons  bring  objects  close  to  the  eye  in  order 
to  see  them  ? 

Because  the  distance  between  the  front  and  back  of 
the  eye  is  so  great,  that  the  image  of  distant  objects  is 
formed  m  front  of  the  retina;  but  when  objects  are 
brought  near  to  the  eye,  their  image  is  thrown  farther 
made  to  fall  on  the  retina. 


1718    Why  do  old  people  hold  objects  far  off  in  order  to  see  them  better  t 

Because  the  distance  between  the  front  and  back  of 
their  eyes  is  not  great  enough  /  when,  however,  objects 


266  SCIENCE    OF   COMMON   THINGS. 

Use  of  the  e}rebrows  and  eyelashes. 

are  held  farther  off,  it  compensates  for  this  defect,  and 
a  perfect  image  is  formed  on  the  retina. 

Birds  of  prey  are  enabled  to  adjust  their  eyes  so  as  to  see  objects  at  a 
great  distance,  and  again  those  which  are  very  near.  The  first  is  accom- 
plished by  means  of  a  muscle  in  the  eye,  which  enables  them  to  flatten 
the  cornea  by  drawing  back  the  crystalline  lens ;  and  to  enable  them  to 
perceive  distinctly  very  near  objects,  their  eyes  are  furnished  with  a 
flexible  bony  rim.  by  which  the  cornea  is  thrown  forward  at  will,  and  the 
eye  thus  rendered  near-sighted. 

1*710  Why  do  persons  who  are  short-sighted  in  youth,  gradually  have 
this  failing  corrected  as  they  grow  old  ? 

They  are  short-sighted  because  the  cornea  of  the  eye 
is  too  globular  ;  but  as  age  advances,  the  fluids  are  not 
secreted  as  before,  the  eye  becomes  flattened,  and 
natural  sight  is  again  restored. 

1730  What  is  the  use  of  the  eyebrows  ? 

The  eyebrows  defend  the  eyes  from  too  strong  a  light, 
and  serve  to  turn  away  substances  which  might  other- 
wise fall  into  the  eye. 

1731  What  is  the  use  of  the  eyelashes? 

The  eyelashes  guard  the  eye  from  danger,  and  pro- 
tect it  from  dust  or  insects  floating  or  flying  in  the  atmo- 
sphere. 

17*33   Why  is  the  eye  pained  by  a  sudden  light  f 

Because  the  nerve  of  the  eye  is  burdened  with  rays 
before  the  pupil  has  had  time  to  contract. 

1733  What  is  the  pupil  of  the  eye  ? 

The  circular  black  opening  in  front  of  the  eye. 

1734  Why  does  it  give  us  pain  if  a  bright  light  is  brought  suddenly 
towards  us  at  night-time  ? 

Because  the  pupil  of  the  eye  dilates  very  much  in 
the  dark  in  order  to  admit  more  rays. 

When  therefore  a  light  is  brought  suddenly  before  us,  the  enlarged 
pupils  overload  the  optic  nerves  with  rays,  which  causes  pain. 

1735  Why  can  we  bear  the  light Rafter  a  few  moments  f 

Because  the  pupils  contract  again  almost  instantly, 
and  adjust  themselves  to  the  quantity  of  light  which 
falls  upon  them. 

1736  Why  can  we  see  nothing  when  we  leave  a  well-lighted  room,  and 
go  into  the  darker  road  or  street  ? 


SCIENCE   OF   COMMON   THINGS.  267 

Vision  in  the  light  and  in  darkness.  Cats — how  see  in  the  dark. 

Because  the  pupil  (which  contracted  in  the  bright 
room)  does  not  dilate  instantaneously ;  and  the  con- 
tracted pupil  is  not  able  to  collect  rays  enough  from  the 
darker  road  or  street  to  enable  us  to  see  objects  before  us. 

IT'S?  How  does  light  cause  the  pupil  of  the  eye  to  contract  ? 

The  pupil  of  the  eye  is  a  round  hole  in  the  midst  of 
a  movable  muscular  curtain  or  screen,  called  the  iris. 
"When  too  much  light  falls  on  the  nervous  retina  at  the 
back  of  the  eye,  it  irritates  it ;  and  this  irritation  is 
conveyed  to  the  muscular  rings  composing  the  curtain 
by  small  nervous  fibres,  causing  them  to  contract. 

17*38    Why  do  we  see  better  when  we  get  used  to  the  dark  f 

Because  the  pupil  dilates  again,  and  allows  more  rays 
to  pass  through  its  aperture.;  in  consequence  of  which 
we  see  more  distinctly. 

17*39  If  we  look  at  the  sun  for  a  few  moments,  why  do  all  oilier  things 
appear  dark  f 

Because  the  nerve  of  the  eye,  by  looking  at  the  sun, 
is  so  affected  by  the  intensity  of  the  light  that  it  requires 
a  few  moments  to  recover  its  former  sensibility. 

17*30  Why  can  we  see  the  proper  colors  of  every  object  again  after  a 
few  minutes  f 

Because  the  eye  again  recovers  its  sensibility,  and 
accommodates  itself  to  the  light  around. 

17*31    Why  can  tigers,  cats,  and  owls  see  in  the  dark  f 

Because  they  have  the  power  of  enlarging  the  pupil 
of  their  eyes  so  as  to  collect  the  scatterea  rays  of  light ; 
in  consequence  of  which  they  can  see  distinctly  when  it 
is  not  light  enough  for  us  to  see  anything  at  all. 

17*33  Why  is  it  that  when  we  press  slightly  upon  the  ball  of  either  eye, 
while  viewing  an  object,  we  see  double?  \ 

Because  the  pressure  of  the  finger  prevents  the  ball 
of  one  eye  from  following  the  motion  of  the  other,  and 
the  axis  of  vision  in  each  eye  being  different,  we  see 
two  images. 

17*33  Do  persons  who  squint  see  double  1 

They  do  /  but  practice  gives  them  p^ower  of  attending 
to  the  sensation  of  only  one  eye  at  a  time. 


268  SCIENCE   OF   COMMON   THINGS. 

Cause  of  squinting.  We  see  images  and  not  objects  themselves. 


17*34    What  is  the  cause  of  strabismus,  or  squinting  ? 

The  inability  of  one  eye  to  follow  the  motions  of  the 
other ;  this  may  arise  from  habit,  imperfect  power  in 
one  eye,  or  some  defect  in  the  muscular  movements. 

17*35  Why,  when  the  eye  is  violently  struck  or  pressed  upon,  do  we  seem 
to  see  light  ? 

Because  the  pressure  communicated  to  the  optic 
nerve  causes  a  violent  and  momentary  sensation  of 
light. 

17*3G    When  we  say  we  see  an  object,  what  do  we  in  fact  do  f 

The  mind  is  only  taking  cognizance  of  the  picture  or 
impression  made  on  the  retina. 

17*37*  If  the  mind,  in  seeing  an  object,  sees  in  reality  only  a  picture 
yainted  on  the  back  of  the  retina,  how  is  it  enabkd  to  judge  of  magnitudes, 
distances,  etc.,  the  picture  being  on  a  comparatively  fiat  surface  f 

It  is  only  by  experience.  "  I  see  men  as  trees  walk- 
ing," said  the  man  born  blind,  when  restored  to  sight. 

17*33  Would  a  person  whose  eyes,  although  perfect,  had  been  covered  up 
from  infancy  to  maturity,  be  able  to  see  ?  that  is,  comprehend  any  scene  or 
prospect  on  which  he  first  opened  his  eyes  ? 

He  would  see  the  objects,  but  could  no  more  under- 
stand them  than  a  child  understands  the  printed  page 
on  which  it  looks,  although  every  word  is  clear  and 
distinct. 

17*39  Do  we  see  the  same  lines  and  surfaces  of  an  object  alike  wicheach 
eye? 

"We  do  not. 

We  may  convince  ourselves  that  we  do  not,  by  placing  two  candles,  fo? 
example,  in  such  &  position,  that  when  they  are  looked  at  with  the  right  eye, 
one  is  made  to  cover  the  other ;  if  now  we  close  the  right  eye  and  look  at 
them  with  the  left,  the  most  remote  candle  will  be  no  longer  screened  by 
the  front  one,  but  will  be  seen  about  an  inch  to  the  left  of  it. 

17*40  Why  cannot  we  count  the  posts  of  a  fence  when  wt  are  riding 
rapidly  in  a  railroad  car  ? 

Every  impression,  according  to  the  intensity  of  its 
effects,  remains  for  a  certain  length  of  time  on  the 
retina,  and  a  measurable  period  is  necessary  to  produce 
the  impression.  The  light  from  each  post  falls  upon 
the  eye  in  such  rapid  succession,  that  the  different 
images  become  confused  and  blended,  and  we  do  not 
obtain  a  distinct  vision  of  the  particular  parts. 


SCIENCE   OF   COMMON  THINGS.  269 

Why  the  sun  and  moon  seem  larger  on  the  horizon  than  overhead. 

17*41  Why  do  the  sun  and  moon  seem  larger  at  their  rising  and  setting 
than  at  any  other  time  f  » 

The  appearance  is  an  illusion,  in  consequence  of  ter- 
restrial objects  being  placed  in  close  comparison  with 
them  at  one  time,  and  not  at  the  other. 

1*74:3  Is  this  illusion  an  optical  one,  or  a  mental  illusion  t 

A  mental  one,  since  the  organs  of  vision  do  not  pre- 
sent to  us  a  larger  image  of  the  moon  or  sun  in  the 
horizon  than  in  the  zenith. 

17*43   What  do  we  mean  by  the  horizon  ? 

The  circle  or  line  where  the  earth  and  sky  appear  to 
meet. 

1744   What  do  we  mean  by  the  zenith  f 

The  point  or  part  of  the  heavens  immediately  over- 
head. 

17*45  Is  the  moon  nearer  or  farther  from  us  when  upon  the  horizon  f 

When  the  moon  is  on  the  horizon,  it  is  about  four 
thousand  miles  farther  from  us  than  when  in  the  zenith  ; 
its  apparent  diameter,  therefore,  instead  of  appearing 
larger,  ought  to  appear  about  a  sixtieth  part  less. 

17*46  Why  are  we  so  often  mistaken  in  respect  to  the  actual  distance 
of  a  conflagration  at  night  ? 

Light  radiating  from  a  centre  rapidly  weakens  as  the 
distance  from  the  centre  increases,  being,  for  instance, 
only  one-fourth  part  as  intense  at  double  the  distance. 
The  eye  learns  to  make  these  allowances,  and  by  the 
clearness  and  intensity  of  the  light  proceeding  from  the 
object,  judges  with  considerable  accuracy  of  the  com- 
parative distance.  But  a  fire  at  night  appears  uncom- 
monly brilliant,  and  therefore  seems  near. 

17*47*  Why  does  the  evening  star  rising  over  a  hill-top  appear  as  if 
situated  directly  over  the  top  of  the  eminence  ? 

Because  we  make  brightness  and  clearness  to  depend 
on  contiguity,  as  it  ordinarily  "does ;  and  as  the  star  is 
bright,  we  unconsciously  think  it  near  us. 

1748  What  is  the  cause  of  colors  t 

The  action  of  light. 

1749  How  is  thit  proved  ? 

12* 


270  SCIENCE   OF   COMMON   THINGS. 

Color  and  its  cause.       Why  are  some  bodies  red  and  others  white,  black,  &c.  ? 


In  the  dark,  bodies  have  no  color,  and  in  the  light 
their  colors  may  be  altered  by  subjecting  to  certain  mo- 
difications the  light  by  which  they  are  rendered  visible. 
Thus  a  blue  piece  of  cloth  in  a  red  light  will  appear  red. 

17*50  Why  is  it  that  we  find  it  difficult  to  distinguish  colors  ~by  candle- 
light? 

Because  we  have  modified  the  light  upon  which  the 
full  effect  of  the  color  depends. 

17*51    What  then  is  the  true  definition  of  color  ? 

The  color  of  a  substance  is  the  effect  of  light  on  a 
surface  adapted  to  reflect  its  particular  color. 

17*53    Why  do  some  things  reflect  one  color,  and  some  another  f 

Because  the  surface  of  things  is  so  differently  consti- 
tuted, both  physically  and  chemically. 

17*53   Why  is  a  rose  red  ? 

Because  the  surface  of  a  rose  absorbs  the  Hue  and 
yellow  rays  of  light,  and  reflects  only  the  red. 

17*54   Why  are  some  things  black  f 

Because  they  absorb  all  the  rays  of  light,  and  reflect 
none. 

1755  Is  black  a  color  f 

It  is  not  /  it  is  the  absence  of  color. 

17*56    Why  are  some  things  white  f 

Because  they  absorb  none  of  the  rays  of  light,  but 
reflect  them  all. 

17*57*   Why  are  clouds,  snow,  sugar,  and  salt  white  f 

Because  they  reflect  'back  unchanged  the  white  light 
which  strikes  upon  them. 

17*58   Why  are  not  the  crystals  of  frost  and  snow  transparent  like  icef 

The  crystals  of  frost  and  snow  are  not  solid,  but  they 
contain  air ;  hence  their  brilliant  whiteness  :  for  the  air 
preventing  the  ready  transmission  of  light  through  the 
crystals,  the  rays  are  copiously  reflected,  from  the  mass 
of  crystals. 

17*59    Why  is  the  darkness  of  night  diminished  by  the  presence,  of  snow  f 

Because  the  snow  reflects,  instead  of  absorbing,  like 


SCIENCE   OF   COMMON   THINGS*  271 

Origin  of  color  in  leaves  of  trees.  Why  is  the  sky  blue  ? 

the  bare  ground,  the  faint  light  that  proceeds  from  the 
sky. 

176O   Why  are  the  leaves  of  plants  green  f 

Because  a  peculiar  chemical  principle,  called  chloro- 
phyl, is  formed  within  their  cells,  which  has  the  property 
of  absorbing  the  red  rays,  and  of  reflecting  the  blue  and 
yellow,  which  mixture  produces  green. 

17G1    Why  are  leaves  a  light  green  in  spring  f 

Because  the  chlorophyl  is  not  fully  formed. 

17(33    Why  do  leaves  turn  brown  in  autumn  f 

Because  the  chlorophyl  undergoes  decay,  and  is  not 
replaced  as  it  is  in  spring. 

1763  Why  do  all  things  appear  black  in  the  dark  f 

In  the  dark  there  is  no  color,  because  there  is  no  light 
to  be  absorbed  or  reflected,  and  therefore  none  to  be 
decomposed. 

Of  course,  in  certain  degrees  of  darkness,  all  objects  are  actually  invi- 
sible. The  question  refers  to  that  peculiar  degree  of  darkness  when  the 
forms  of  objects  may  be  seen,  but  not  their  hues. 

1764  Why  does  the  sky  appear  blue  ? 

Because  the  atmosphere  absorbs  the  red  and  yellow 
rays,  and  transmits  the  blue. 

1765  Why  does  the  sun  most  generally  fade  artificial  colors  f 

Generally  the  loss  of  color  arises  from  the  oxidation 
of  the  substances  used  in  dyeing ;  as  tarnish  and  rust  are 
an  oxidation  of  metals.  Sometimes,  however,  the 
ingredients  of  the  dye  are  otherwise  decomposed  by  the 
sun ;  and  the  color  (which  is  due  to  a  combination  of 
ingredients)  undergoes  a  change  as  soon  as  the  sun 
deranges  or  destroys  that  combination. 

1766  What  remarkable  correspondence  is  there  between  the  geographical 
position  of  a  region,  and  the  colors  of  its  plants  and  animals  f 

In  the  tropics,  where  the  sun  shines  longest  and 
brightest,  the  darkest  green  prevails  over  the  leaves  of 
plants,  the  flowers  and  fruits  are  colored  brightly,  and 
the  plumage  of  the  birds  is  of  the  richest  description. 

1767  What  is  the  natural  coloration  exhibited -in  temperate  climates  f 

In  temperate  climates  everything  is  of  a  more  sub- 


272  SCIENCE   OF  COMMON   THINGS. 


Colors  in  different  regions  of  the  earth.  Contrasts  of  colors. 

dued  variety  •  the  flowers  are  less  bright ;  the  prevail- 
ing tint  of  the  birds  is  brown ;  and  the  dresses  of  the 
inhabitants  are  sombre. 

IT'S 8  How  is  this  corfespondence  further  exemplified  in  the  Arctic  and 
Antarctic  regions  ? 

Here  there  is  little  color  in  natural  objects  ;  the  few 
flowers  are  white  or  yellow  /  and  the  animals  are  almost 
uniformly  Hack  or  white. 

17*69  In  what  part  of  the  ocean  do  we  find  the  brightest  shells  and  sea- 
weeds ? 

Near  the  shore,  in  shallow  water,  where  the  influence 
of  light  is  greatest. 

17*  7*0    What  fishes  are  distinguished  for  the  brilliancy  of  their  colors? 

Those  that  swim  near  the  surface;  whereas  those 
which  live  at  greater  depths  are  gray,  brown,  and  black. 

17*7*1  What  is  the  appearance  of  the  sea-weeds  and  animals  that  live  at 
great  depths  of  the  ocean  ? 

They  are  nearly  colorless. 

17*7*3  Why  is  grass  growing  under  a  covering  of  a  white  or  yellowish 
white  color  f 

Because  it  is  secluded  from  the  light,  whose  presence 
and  action  is  necessary  for  the  production  of  the  material 
which  imparts  to  it  its  green  color. 

17*7*3  Of  the  various  rays  composing  solar  light,  which  are  the  most 
visible  to  the  human  eye  ? 

The  yellow. 

17*7*4   Which  have  the  greatest  heating  effect  f 

The  faint  red  rays. 

17*7*5  Why  does  a  dress  composed  of  cloths  of  different  colors,  look  well 
much  longer,  although  worn,  than  one  of  only  a  single  color,  the  character  of 
the  cloth  in  both  instances  being  identical  ? 

It  is  owing  to  the  effect  of  contrast  between  the 
colors.  If  a  dress  is  composed  of  cloths  of  two  colors, 
as  red  and  green,  orange  and  blue,  yellow  and  violet, 
they  will  mutually  heighten  the  effect  of  each,  and  make 
each  portion  appear  to  the  best  advantage. 

17*7*0  Why  will  stains  be  less  visible  on  a  dress  of  different  colors,  than 
on  one  composed  of  only  a  single  color  ? 

Because  there  exists  in  general  a  greater  contrast 


SCIENCE   OF   COMMON   THINGS. 


Contrasts  of  colors  In  dress.  Arrangement  of  bouquets. 

among  the  various  parts  of  the  first-named  dress,  than 
between  the  stain  and  the  adjacent  part,  and  this  differ- 
ence renders  the  stain  less  apparent  to  the  eye. 

177  7  Why  can  a  coat,  waistcoat,  and  pants  of  the  same  color  be  worn 
with  advantage  together  only  when  they  are  new  f 

Because  as  soon  as  one  of  them  loses  its  freshness 
from  having  been  worn  longer  than  the  others,  the 
difference  will  increase  by  contrast. 

1778  Give  an  illustration. 

A  pair  of  new  black  pants,  worn  with  a  vest  of  the 
same  color,  which  is  old  and  rusty,  will  make  the  tinge 
of  the  latter  appear  more  conspicuous,  and  at  the  same 
time  the  black  of  the  pants  will  appear  more  brilliant. 
White  and  other  light-colored  trowsers  would  produce 
a  contrary  effect. 

1779  What  is  the  general  law  upon  which  the  harmony  of  colors 
depends  ? 

Every  color  when  placed  beside  another  color  is 
changed,  appearing  different  from  what  it  really  is; 
and  it  moreover  equally  modifies  the  colur  with  whicn 
it  is  in  proximity. 

1780  What  effect  has  rose-red  upon  a  rosy  complexion  f 

It  causes  it  to  lose  some  of  its  freshness. 

1781  For  fair  complexions,  deficient  in  rose,  which  color  is  most  favor* 
abkf 

A  delicate  green.,. 

17SS    What  effect  has  black  drapery  upon  the  color  of  the  skin  1 

It  makes  it  appear  whiter. 

1783  What  rule  should  be  observed  in  the  grouping  of  flowers  and  the 
preparation  of  bouquets  ? 

"We  must  separate  pink  flowers  from  those  that  are 
either  scarlet  or  crimson ;  orange,  from  orange  yellow 
flowers ;  yellow  flowers  from  greenish-yellow  flowers  ; 
blue  from  violet-blue,  red  from  orange,  pink  from  violet ; 
blue  flowers  from  violet  flowers. 

1784  What  is  the  optical  effect  of  dark  colors  and  black  upon  the  size 
of  the  figure  f 


2  74:  SCIENCE   OF   COMMON  THINGS. 

Most  conspicuous  colors.  Colors  of  animals  adapted  to  their  necessities. 

It  causes  it  to  appear  smaUer  /  therefore  these  colors 
are  most  suitable  for  stout  persons. 

1785  What  effect  do  white  and  light-colored  dresses  have  upon  the  size 
of  the  figure  ? 

They  cause  it  to  appear  larger. 

178Q   What  effect  do  large  patterns  in  dress  make  f 

They  make  the  figure  look  shorter. 

1787  What  is  the  effect  of  narrow  longitudinal  stripes  in  dress  t 

They  add  to  the  apparent  height  of  the  figure. 

1788  What  is  the  effect  of  fwrizontal  stripes  ? 

The  effect  of  horizontal  stripes  is  opposed  to  that  of 
longitudinal,  and  under  every  condition  they  are  un- 
graceful. 

1789  What  colors  are  most  conspicuous  in  battle  f 

It  has  been  found  by  numerous  observations  that  red 
is  the  most  fatal  color,  and  the  least  fatal  is  a  light  grey. 

1790  What  curious  provision  for  the  protection  of  animals  does  nature 
appear  to  make  ? 

She  appears  to  have  adapted  the  color  of  the  creature 
to  its  haunts  in  such  a  way  as  tends  to  preserve  it  from 
injury.  Caterpillars  and  insects  which  feed  on  leaves 
are  generally  of  the  color  of  the  leaves.  As  long  as 
they  remain  still,  it  is  almost  impossible  to  distinguish 
the  grasshopper  from  the  herbage  on  which  it  rests. 

1791  What  curious  change  is  noticed  in  the  color  of  animals  inhabiting 
the  Arctic  regions  f 

During  the  snows  of  winter,  foxes,  hares,  and  some 
varieties  of  birds  are  white  ;  when  the  ground  is  free 
from  snow  in  summer,  they  are  of  a  'brown  color. 


SCIENCE   OF   COMMON   THINGS.  275 

What  is  electricity  ?  Means  of  exciting  electricity. 


PART  VIII. 

ELECTRICITY,  GALVANISM,  MAGNETISM,  AND 
ELECTRO-MAGNETISM, 


CHAPTEE   I. 

ELECTRICITY. 
1793   What  is  electricity  t 

Electricity  is  one  of  those  imponderable  agents  that 
appear  to  be  diffused  through  all  nature,  existing  in  all 
substances  without  affecting  their  volume  or  their  tem- 
perature, or  giving  any  indication  of  its  presence  when 
in  a  latent  state.  When,  however,  it  is  liberated  from 
this  repose,  it  is  capable  of  producing  the  most  sudden 
and  destructive  effects,  or  of  exerting  powerful  influences 
by  a  quiet  and  long-continued  action. 

1*793  How  may  electricity  be  called  into  activity  f 

By  mechanical  power,  by  chemical  action,  by  heat, 
and  by  magnetic  influence. 

17*94   What  is  the  most  ordinary  way  of  exciting  electricity  f 

By friction. 

17*95  Do  we  know  any  reason  why  the  means  above  enumerated  should 
develope  electricity  from  its  latent  condition? 

We  are  entirely  ignorant  upon  this 'subject. 

17*96  When  you  rub  apiece  of  paper  with  India-rubber,  why  does  it 
adhere  to  the  table  f 

Because  tlie  friction  of  the  India-rubber  against  the 
surface  of  the  paper  developes  electricity,  to  which  this 
adhesiveness  is  mainly  to  be  attributed. 

17*97*  Does  electricity  present  any  appearance  by  which  it  can  be  "known  f 

No ;  electricity,  like  heat,  is  in  itself  invisible,  though 
often  accompanied  by  both  light  and  heat. 


276  SCIENCE  OF   COMMON   THINGS. 

Electrified  and  non-electrified  bodies. 


17*93  When  a  substance,  by  friction  or  by  any  other  means,  acquires 
the  property  of  attracting  other  bodies,  in  what  state  is  it  said  to  be? 

It  is  said  to  be  electrified^  or  electrically  excited  /  and 
its  motion  towards  other  bodies,  or  of  other  bodies  to- 
wards it,  is  ascribed  to  a  force  called  electric  attraction. 

17*09  Does  an  electrified  body  exercise  any  other  influence  than  an, 
attractive  onef 

It  does ;  for  it  will  be  found  that  light  substances, 
after  touching  the  electrified  body,  will  recede  from  it 
just  as  actively  as  they  approached  it  before  contact. 
This  is  termed  electric  repulsion. 

Thus,  if  we  take  a  dry  glass  rod,  rub  it 
well  with  silk,  and  present  it  to  a  light  pith 
ball,  or  feather,  suspended  from  a  support 
by  a  silk  thread,  the  ball  or  feather  will  be 
attracted  towards  the  glass,  as  seen  at  G, 
Fig.  81.  After  it  has  adhered  to  it  a  mo- 
ment, it  will  fly  off,  or  be  repelled,  as  P'  from 
G'.  The  same  will  happen  if  sealing-wax 
be  rubbed  with  dry  flannel,  and  a  like  ex- 
Fig.  81.  periment  made ;  but  with  this  remarkable 
difference,  that  when  the  glass  repels  the 

ball,  the  sealing-wax  attracts  it,  and  when  the  wax  repels,  the  glass  will 
attract.  These  phenomena  are  examples  of  electrical  attraction  and 
repulsion. 

1800  What  is  a  non-electrified  body  f 

One  that  holds  its  own  natural  quantity  of  electricity 
undisturbed. 

1801  What  happens  when  an  electrified  body  touches  one  that  is  non- 
electrified  f 

The  electricity  contained  in  the  former  is  transferred 
in  part  to  the  latter. 

Thus,  on  touching  the  end  of  a  suspended  silk-thread  with  a  piece  of 
excited  wax,  the  silk  will  be  excited,  as  will  be  shown  by  its  moving 
towards  a  book,  piece  of  metal,  or  any  other  object  placed  near  it. 

18OS  Do  all  bodies  conduct  or  allow  electricity  to  pass  through  them 
equally  well? 

Although  there  is  no  substance  that  can  entirely  pre- 
vent the  passage  of  electricity,  nor  any  that  does  not 
oppose  some  resistance  to  its  passage,  yet  it  moves  with 
a  much  greater  facility  through  a  certain  class  of  sub- 
stances than  through  others.  Those  substances  which 


SCIENCE   OF   COMMON   THINGS. 


277 


Conductors  and  non-conductors  of  electricity. 


Electrical  machines. 


facilitate  its  passage  are  called  conductors ;  those  that 
retard  or  almost  prevent  it,  are  called  non-conductors. 

1803  What  substances  are  good  conductors  of  electricity  ? 

The  metals,  charcoal,  the  earth,  water,  and  most  fluids, 
except  oils,  the  human  body,  etc.,  are  good  conductors. 

1804  What  substances  obstruct  the  passage  of  electricity,  or  are  "non- 
conductors ?" 

Glass,  resin,  oil,  silk,  sulphur,  dry  air,  etc.,  etc.,  are 
non-conductors. 

1805  What  is  an  electrical  machine  f 

An  electrical  machine  is  an  arrangement  by  which 
quantities  of  electricity  can  bexollected  and  discharged. 

The  electrical  machine  most  usu- 
ally employed  consists  of  a  large 
circular  plate  of  glass,  see  Fig.  82, 
mounted  upon  a  metallic  axis,  and 
supported  upon  pillars  fixed  to  a 
secure  base,  so  that  the  plate  can, 
by  means  of  a  handle,  W,  be  turned 
with  ease.  Upon  the  supports 
of  the  glass,  and  fixed  so  as  to 
press  easily  but  uniformly  on  the 
plate,  are  four  rubbers,  marked  r  r 
r  r  in  the  figure  ;  and  flaps  of  silk, 
s  5,  oiled  on  one  side,  are  attached 
to  these,  and  secured  to  fixed  sup- 
ports by  several  silk  cords.  "When 
the  machine  is  put  in  motion,  these 
flaps  of  silk  are  drawn  tightly 
against  the  glass,  and  thus  the 
friction  is  increased,  and  electricity 
excited.  The  points  p  p  collect 
the  electricity  from  the  glass,  and 
convey  it  to  the  conductor,  c,  which  is  sup- 
ported by  the  glass  rod  g. 

Fig.  83  represents  another  form  of  an 
electrical  machine,  constructed  on  similar 
principles.  S  being  a  glass  cylinder  turn- 
ing on  an  axis,  Y  the  conductor,  F  the 
rubber,  A  A  supports. 

1806  What  is  the  theory  of  electricity 
most  generally  adopted  ? 

The  theory  proposed  by  Dr. 


ine  tneory  proposed  by  Ur. 
Franklin:  this  supposes  the  ex- 
istence of  a  single,  imponderable 


Fig,  83. 


278  SCIENCE   OF  COMMON   THINGS. 


Positive  and  negative  electricity.  Velocity  of  electricity. 

fluid,  equally  distributed  throughout  nature :  every 
substance  being  so  constituted  as  to  retain  a  certain 
quantity  of  this  agent.  Any  disturbance  of  the  natural 
state  of  a  body  produces  evidences  of  electricity. 

ISOT*  Does  electricity  seem  to  exist  in  two  different  states  or  conditions  f 

It  does ;  and  to  designate  these  two  conditions,  the 
terms  positive  and  negative  have  been  employed.  Thus 
a  body  which  has  an  overplus  of  electricity  is  called  posi- 
tive, and  one  that  has  less  than  its  natui^l  quantity  is 
called  negative. 

ISO 8  Do  light,  heat,  and  electricity  appear  to  have  some  properties  in 
common  f 

They  do  /  each  may  be  made,  under  certain  circum- 
stances, to  produce  or  excite  the  other.  All  are  so  light, 
subtle,  and  diffusive,  that  it  has  been  found  impossible 
to  recognise  in  them  the  ordinary  characteristics  of 
matter.  Some  suppose  that  light,  heat,  and  electricity 
are  all  modifications  of  some  common  principle. 

18O9  Why  does  the  fur  of  a  cat  sparkle  and  crackle  when  rubbed  with 
the  hand  in  cold  weatlier  ? 

Because  the  friction  between  the  hand  and  fur  pro- 
duces an  excitation  of  negative  electricity  in  the  hand 
and  positive  in  the  fur,  and  an  interchange  of  the  two 
causes  a  spark,  with  a  slight  noise. 

1S1O   Why  does  this  experiment  work  best  in  very  cold  weather  ? 

Because  the  air  is  then  very  dry,  and  does  not  convey 
away  the  electricity  as  fast  as  it  is  excited ;  if  the  air, 
on  the  contrary,  were  moist,  the  electricity  would  be 
conducted  off  nearly  as  fast  as  it  was  excited  by  friction, 
and  its  effects  would  not  therefore  be  so  manifest. 

1811  With  what  velocity  is  electricity  transmitted  through  good  conduc- 
tors f 

"With  a  velocity  so  great  that  the  most  rapid  motion 
produced  by  art  appears  to  be  actual  rest  when  com- 
pared to  it.  Some  authorities  have  estimated  that  elec- 
tricity will  pass  through  copper  wrire  at  the  rate  of  two 
hundred  and  eighty-eight  thousand  miles  in  a  second 
of  time — a  velocity  greater  than  that  of  light.  The 


SCIENCE   OF   COMMON   THINGS.  279 

Principal  agents  in  nature  exciting  electricity. 

results  obtained,  however,  by  the  United  States  Coast 
Survey,  with  iron  wire,  show  a  velocity  of  from  15,000 
to  20,000  miles  per  second.  » 

1813  What  agents  are  undoubtedly  the  most  active  in  producing  and 
exciting  electricity  in  the  operations  of  nature  f 

The  light  and  heat  of  the  suds  rays. 

1813  It  has  become  the  habit  with  many  to  ascribe  to  electricity  the 
agency  of  phenomena  in  the  natural  world,  the  cause  of  which  may  not  be 
apparent:  is  there  any  reason  for  this? 

There  certainly  is  not  :  electricity  is  diffused  through 
all  matter,  and  is  ever  active,  and  many  of  its  pheno- 
mena cannot  be  satisfactorily  explained  ;  but  it  is  go- 
verned, like  all  other  forces  of  nature,  by  certain  fixed 
laws,  and  it  is  by  no  means  a  necessary  agent  in  all  the 
operations  of  nature. 

It  argues  great  ignorance  to  refer  without  examination  every  mysteri- 
ous phenomenon  to  the  influence  of  electricity. 

1814  Do  some  animals  have  the  power  of  exciting  electricity  within 
themselves  f 

There  are  certain  animals  which  are  gifted  with  the 
extraordinary  power  of  producing  electncal  phenomena 
by  an  effort  of  muscular  or  nervous  energy.  Among 
these  the  electrical  eel  and  the  torpedo  are  most  re- 
markable. 

1815  How  powerful  a  charge  of  electricity  can  the  electrical  eel  send 
forth  when  in  full  vigor  f 

Sufficient  to  knock  down  a  man  or  stun  a  horse. 

1810  Is  the  electricity  generated  by  these  animals  the  same  as  that  occa- 
sioned by  tlie  ordinary  electrical  machine  ? 

It  is  the  same,  and  produces  the  same  effects. 


Do  vital  action  and  muscular  movements  in  man  and  animals 
give  rise  to  electricity  f 

They  do  ;  and  it  can  be  shown  by  direct  experiment 
that  a  person  cannot  even  contract  the  muscles  of  the 
arm  without  exciting  an  electrical  action. 

1818  Does  change  of  form  or  state  in  bodies  generally  produce  electrical 
excitation  ? 

Change  of  form  or  state  is  one  of  the  most  powerful 
methods  of  exciting  electricity. 


280  SCIENCE    OF   COMMON   THINGS. 

Lightning.  Three  forms  of  lightning. 


Water,  in  passing  into  steam  by  artificial  heat,  or  in  evaporating  by  the 
action  of  the  sun  or  wind,  generates  large  quantities  of  electricity.  The 
crystallization  of  solids  from  liquids,  all  changes  of  temperature,  the 
growth  and  decay  of  vegetables,  are  also  instrumental  in  producing  elec- 
trical phenomena. 

1S1Q    What  is  lightning  f 

Lightning  is  accumulated  electricity,  generally  dis- 
charged from  the  clouds  to  the  earth,  but  sometimes 
from  the  earth  to  the  clouds. 

1S3O    What  causes  the  discharge  of  an  electric  cloud? 

When  a  cloud  overcharged  with  electric  fluid  ap- 
proaches another  which  is  undercharged,  the  fluid 
rushes  from  the  former  into  the  latter,  till  both  contain 
the  same  quantity. 

18J31  Is  there  any  other  cause  of  lightning  besides  the  one  just  men- 
tioned ; 

Yes ;  sometimes  mountains,  trees,  and  steeples  will 
discharge  the  lightning  from  a  cloud  floating  near,  and 
sometimes  the  electricity  passes  from  the  earth,  into 
the  clouds. 

1833  How  high  are  the  lightning  clouds  from  the  earth? 

Sometimes  they  are  elevated  four  01*  five  miles  high, 
and  sometimes  actually  touch  the  earth  with  one  of 
their  edges  ;  but  they  are  rarely  discharged  in  a  thun- 
der storm  when  they  are  more  than  seven  hundred 
yards  above  the  surface  of  the  earth. 

1833    What  is  a  thunder  storm  ? 

The  disturbance  caused"  in  the  air  when  successive 
discharges  of  accumulated  electricity  take  place. 

1S34  Into  how  many  kinds  has  lightning  been  divided  ? 

Three. 

1835  What  are  they  ? 

The  zig-zag  lightning,  sheet  lightning,  and  hall  light- 
ning. 

1836  Why  is  lightning  sometimes  forked  ? 

Because  the  lightning  cloud  is  at  a  great  distance  ; 
and  the  resistance  of  the  air  is  so  great  that  the  electri- 
cal current  is  diverted  into  a  zig-zag  course. 


SCIENCE    OF   COMMON   THINGS.  281 


Sheet  and  heat  lightning.  Duration  of  a  flash  of  lightning. 


1837  How  does  the  resistance  of  the  air  make  the  lightning  zig-zag  ? 

As  the  lightning  condenses  the  air  in  the  immediate 
advance  of  its  path,  it  flies  from  side  to  side,  in  order 
to  pass  where  there  is  the  least  resistance. 

18SS    Why  is  the  flash  sometimes  quite  straight  ? 

Because  the  lightning  cloud  is  near  the  earth,  and  as 
the  flash  meets  with  very  little  resistance,  it  is  not 
diverted  ;  in  other  words,  the  flash  is  straight. 

183Q   What  is  sheet  lightning? 

Either  the  reflection  of  distant  flashes  not  distinctly 
visible  or  beneath  the  horizon,  or  else  several  flashes 
intermingled. 

1830  What  other  form  does  lightning  occasionally  assume  ? 

Sometimes  the  flash  is  globular,  which  is  the  most 
dangerous  form  of  lightning. 

1831  Does  a  discharge  produce  a  flash  when  it  passes  through  good 
conductors  f 

It  does  not,  but  passes  quietly  and  invisibly. 

1S3S   What  is  heat  lightning  f 

Sometimes  it  is  the  reflection  in  the  atmosphere  of 
the  lightnings  of  storms  very  remote,  the  storms  them- 
selves being  so  far  distant  that  their  thunders  cannot 
be  heard.  This  phenomenon  is  also  occasioned  by  the 
play  of  silent  flashes  of  electricity  between  the  earth 
and  the  clouds,  the  amount  of  electricity  developed  not 
being  sufficient  to  produce  any  other  effects  than  the 
mere  flash  of  light. 

1833  Why  is  lightning  more  common  in  summer  and  in  autumn  than 
in  spring  and  winter  f 

Because  the  heat  of  summer  and  autumn  produces 
great  evaporation,  and  the  conversion  of  water  into 
vapor  always  developes  electricity. 

1834  How  long  is  the  duration  of  a  flash  of  lightning  f 

Arago  has  demonstrated  that  it  does  not  exceed  the 
millionth  part  of  a  second. 

1835  With  ivhat  velocity  is  lightning,  or  the  electric  fluid  which  gives 
rise  to  its  appearance,  supposed  to  move  f 


282  SCIENCE    OF   COMMON    THINGS. 


Places  dangerous  in  a  thunder  storm.  How  a  tree  influences  lightning. 

Not  less  than  two  hundred  and  fifty  thousand  miles 
per  second. 

1836    Why  does  lightning  sometimes  kill  men  and  leasts  f 

Because,  when  the  electric  current  passes  through  a 
man  or  beast,  it  produces  so  violent  an  action  upon  the 
nervous  system,  that  it  destroys  life. 

1337*    When  is  a  person  struck  dead  by  lightning  1 

Only  when  his  body  forms  a  part  of  the  lightning's 
path  j  that  is,  when  the  electric  fluid  (in  its  way  to  the 
earth)  actually  passes  through  his  body. 

1838  Wliat  places  are  most  dangerous  during  a  thunder  storm  f 

It  is  very  dangerous  to  be  near  a  tree  or  lofty  building. 

1839  Why  is  it  dangerous  to  be  near  a  tree  or  lofty  building  during  a 
thunder  storm  f 

Because  a  tall,  pointed  object  (like  a  tree  or  spire) 
will  frequently  discharge  a  lightning  cloud  ;  and  if  any 
one  were  standing  near,  the  lightning  might  diverge 
from  the  tree  and  pass  through  the  fluids  of  the  human 
body. 

1S4O  How  can  a  tree  or  spire  discharge  a  lightning  cloud  f 

A  lightning  cloud,  floating  over  a  plain,  may  be  too 
far  off  to  be  discharged  by  it ;  but  as  a  tree  or  spire 
would  shorten  this  distance,  it  might  no  longer  be  too 
far  off  to  be  discharged. 

For  example :  If  a  lightning-cloud  were  seven  hundred  yards  above  the 
,  earth,  it  might  be  too  far  off  to  be  discharged ;  but  a  tree  or  spire  fifty 
yards  high  would  make  the  cloud  only  six  hundred  and  fifty  yards  off  a 
conductor ;  in  consequence  of  which  the  cloud  might  be  instantly  dis- 
charged. 

1841  What  parts  of  a  dwelling  are  most  dangerous  during  a  thunder- 
storm f 

The  fireplace  (especially  if  the  fire  be  lighted).  It  is 
also  imprudent  to  sit  close  by  the  walls. 

1843   Why  is  it  dangerous  to  sit  before  afire  during  a  thunder  storm  f 

Because  the  heated  air  and  soot  are  conductors  of 
lightning,  especially  when  connected  with  such  excel- 
lent conductors  as  the  stove,  grate,  or  fire-irons. 

1843  Why  is  it  dangerous  to  lean  against  a  wall  during  a  thunder 
storm  f 


SCIENCE    OF   COMMON   THINGS.  283 

Safest  places  in  a  thunder  storm. 

Because  the  electric  fluid  will  sometimes  run  down 
a  watt,  and  (as  the  body  of  a  person  is  a  better  conduc- 
tor than  a  wall)  would  leave  the  wall  and  run.'  down  the 
body. 

184:4   Why  is  it  dangerous  to  be  in  a  crowd  during  a  thunder  storm  f 

For  two  reasons  :  1.  Because  a  mass  of  people  forms 
a  better  conductor  than  an  individual',  and 

2.  Because  the  vapor  arising  from  a  crowd  increases 
its  conducting  power. 

1845  Why  is  the  danger  increased  by  the  vapor  which  rises  from  a 
crowd? 

Because  vapor  is  a  conductor,  and  the  more  conduc- 
tors there  are,  the  greater  the  danger  will  be. 

1846  If  a  person  be  abroad  in  a  thunder  storm,  what  place  is  the 
safest  ? 

Any  place  about  twenty  or  thirty  feet  from  a  tall 
tree,  building,  or  stream  of  water. 

1847*  Why  would  it  be  safe  to  stand  twenty  or  thirty  feet  from  a  tall 
tree  during  a  thunder  storm  ? 

Because  the  lightning  generally  chooses  tall  trees  as 
conductors,  and  we  should  not  be  sufficiently  near  the 
trees  for  the  lightning  to  diverge  from  them  to  us. 

1848  Why  is  the  middle  of  a  room  more  safe  than  any  other  part  of 
it  in  a  thunder  storm  ? 

Because  the  lightning  (if  it  should  strike  the  room  at 
all)  would  come  down  the  chimney  or  walls  of  the  room; 
and  therefore  the  farther  distant  from  these,  the  better. 

184Q  Why  is  a  mattress,  bed,  or  hearth-rug  a  good  security  against 
injury  from,  lightning  ? 

Because  they  are  all  non-conductors ;  and  as  lightning 
always  makes  choice  of  the  lest  conductors,  it  would  not 
choose  for  its  path  such  things  as  these. 

1850  What  is  the  safest  thing  a  person  can  do  to  avoid  injury  from 
lightning  ? 

Lie  upon  a  led  in  the  middle  of  a  room.  A  led  filled 
with  feathers  is  an  excellent  non-conductor. 

1851  Is  there  not  generally  a  greater  apprehension  of  the  danger  from 
lightning  than  experience  would  justify  ? 

The  apprehension  and  solicitude  respecting  lightning 


284:  SCIENCE   OF   COMMON   THINGS. 

Lightning  conductors.  Their  proper  principle  of  construction. 

are  proportionate  to  the  magnitude  of  the  evils  it  pro- 
duces, rather  than  the  frequency  of  its  occurrence.  The 
chances  of  an  individual  being  killed  by  lightning  are 
infinitely  less  than  those  which  he  encounters  in  his 
daily  .walks,  in  his  occupation,  or  even  during  his  sleep 
from  the  destruction  of  the  house  in  which  he  lodges 
by  fire. 

185S  Why  does  the  lightning  in  its  course  down  a  building  generally 
dart  from  point  to  point,  and  not  follow  a  direct  path  ? 

Because  it  always  takes  in  its  course  the  best  conduc- 
tors ;  and  will  fly  both  right  and  left  in  order  to  reach 
them. 

1853   What  is  a  lightning  conductor  f 

A  metal  rod  fixed  in  the  earth,  running  up  the  whole 
height  of  a  building,  and  rising  in  a  point  above  it. 

185<b   What  metal  is  best,  for  this  purpose  f 

Copper  makes  the  best  conductor. 

1855  What  is  the  use  of  a  lightning  conductor  f 

As  metal  is  a  most  excellent  conductor,  lightning 
(which  makes  choice  of  the  best  conductors)  will  run 
down  a  metal  rod  rather  than  the  walls  of  the  building. 

1856  Why  should  lightning  conductors  be  pointed  f 

Because  points  conduct  electricity  away  silently  and 
imperceptibly.  • 

Blades  of  grass,  ears  of  corn,  and  other  pointed  objects  serve  to  with- 
draw electricity  from  the  clouds. 

1857*  How  far  will  the  beneficial  influence  of  a  lightning  conductor 
extend  f 

It  will  protect  a  space  all  round  four  times  the  length 
of  that  part  of  the  rod  which  rises  above  the  building. 

1858  Give  me  an  example. 

If  the  rod  rises  two  feet  above  the  house,  it  will  pro- 
tect the  building  for  (at  least)  eight  feet  all  round. 

1859  How  can  lightning  conductors  be  productive  of  harm  ? 

If  the  rod  be  broken,  the  electric  fluid  (being  obstruct- 
ed in  its  path)  will  enter  the  building. 

18BO  Is  there  any  other  evil  to  be  apprehended  from  a  lightning  rod  f 

Yes ;  if  the  rod  be  not  large  enough  to  conduct  the 


SCIENCE   OF   COMMON   THINGS.  285 

Franklin's  experiment  with  a  kite.  Identity  of  lightning  and  electricity. 

whole  current  to  the  earth,  the  lightning  will  fuse  the 
metal  and  enter  the  building. 

1861  By' whom  was  Uie  identity  of  lightning  and  electricity  first  esta- 
lliahed  f 

By  Dr.  Franklin,  at  Philadelphia,  in  1752. 

The  manner  in  which  this  fact  was  demonstrated,  was  as  follows: 
Having  made  a  kite  of  a  large  silk  handkerchief  stretched  upon  a  frame, 
and  placed  upon  it  a  pointed  iron  wire  connected  with  the  string,  he  raised 
it  upon  the  approach  of  a  thunder  storm.  A  key  was  attached  to  the 
lower  end  of  the  hempen  string  holding  the  kite,  and  to  this  one  end  of  a 
silk  ribbon  was  tied,  the  other  end  being  fastened  to  a  post.  The  kite 
was  now  insulated,  and  the  experimenter  for  a  considerable  time  awaited 
the  result  with  great  solicitude.  Finally,  indications  of  electricity  began 
to  appear  on  the  string;  and  on  Franklin  presenting  his  knuckles  to  the 
key,  he  raised  an  electric  spark.  The  rain  beginning  to  descend,  wet  the 
string,  increased  its  conducting  power,  and  vivid  sparks  in  great  abun- 
dance flashed  from  the  key. 

18 63  Why  was  the  Me  insulated  when  FranUin  fastened  tlie  key  to  the 
post  with  a  silk  ribbon  ? 

Because  the  silk  was  a  non-conductor ',  and  would  not 
allow  the  electricity  received  upon  the  kite  to  pass  off 
by  means  of  the  string  to  the  ground. 

1863  Was  this  experiment  one  of  great  danger  and  risk  ? 

It  was  ;  because  the  whole  amount  of  electricity  con- 
tained in  the  thunder  cloud  was  liable  to  pass  from  it, 
by  means  of  the  string,  to  the  earth,  notwithstanding 
the  use  of  the  silk  insulator. 

1864  If  a  lightning  rod  is  made  of  iron,  how  large  should  it  be  f 

•Not  less  than  three-quarters  of  an  inch  in  diameter. 

1865  In  what  manner  should  the  rod  be  erected  ? 

The  rod  should  be  continuous  from  the  top  to  the  bot- 
tom, and  an  entire  metallic  communication  should  exist 
throughout  its  whole  length. 

This  law  is  violated  when  the  joints  of  the  several  parts  that  form  the 
Conductor  are  imperfect  and  when  the  whole  is  loosely  put  together. 

1866  How  should  tlie  conductor  be  fastened  to  tfie  building? 

By  wooden  supports. 

-  If  there  are  masses  of  metal  about  the  building,  as  gutters,  pipes,  etc., 
these  should  be  connected  with  the  rod  by  strips  of  metal ;  for  unless  this 
is  done  the  lightning  may  pass  from  the  rod  to  the  metal,  and  enter  the 
building^ 

13 


28(5  SCIENCE   OF   COMMON   THINGS. 

Utility  of  lightning-rods.  What  is  thunder  ? 

1867  How  should  the  lower  end  of  the  rod  be  arranged  ? 

It  should  be  divided  into  two  or  three  branches,  and 
turned  from  the  building. 

The  end  of  the  rod  ought  to  extend  so  far  below  the  surface  of  the 
ground  as  to  reach  earth  that  is  permanently  damp. 

1868  Why  is  it  a  good  plan  to  bury  the  end  of  the  rod  in  powdered 
charcoal  f 

Because  it  preserves  the  iron  from  rust,  and  facili- 
tates the  passage  of  the  electricity. 

1869  Have  we  any  proof  of  the  utility  of  lightning  rods  f 

The  experience  of  a  hundred  years  has  shown  that 
when  all  the  necessary  rules  have  been  observed,  the 
protection  is  perfect,  as  far  as  human  effort  can  avail. 

187*0  Is  a  buikling  more  or  less  liable  to  be  struck  when  furnished  with 
a  good  lightning  conductor  f 

Lightning  conductors  do  not,  as  many  suppose,  attract 
the  lightning  towards  the  building  on  which  they  are 
situated ;  they  simply  direct  its  course,  and  facilitate 
the  passage  of  the  fluid  in  the  most  direct  way  to  the 
earth,  only  when  a  discharge  must  inevitably  occur. 
There  is  no  attraction,  but  the  lightning  takes  the  road 
which  offers  the  least  resistance. 

187*1  Are  lightning  conductors  protective  when  even  no  visible  discharge 
takes  place  f 

They  are;  they  possess  a  very  great  preventive 
power,  and  gradually  and  silently  disarm  the  clouds  by 
conducting  the  electricity  from  them  ;  and  this  process 
commences  as  soon  as  the  cloud  has  approached  a  posi- 
tion vertically  over  the  rod. 

18  7S   What  is  thunder? 

It  is  a  certain  noise  proceeding  apparently  from  the 
clouds,  which  usually  follows,  after  a  greater  or  less 
interval,  the  appearance  of  a  flash  of  lightning. 

187*3  How  is  it  supposed  to  be  occasioned? 

The  usual  explanation  offered  is  a  sudden  displace- 
ment of  the  air  produced  by  the  electrical  discharges  in 
which  the  lightning  is  evolved. 

Others  have  supposed  that  the  passage  of  the  electric  current  creates  a 


SCIENCE   OF  COMMON   THINGS.  287 

What  occasions  the  rolling  of  thunder  ?  Aurora- borealis. 


vacuum,  and  that  the  air  rushing  in  to  fill  it  produces  the  sound.     Any 
explanation  that  has  yet  been  ottered  is  not  altogether  satisfactory. 

1374    What  occasions  the  rotting  of  the  thunder  % 

It  has  been  ascribed  to  the  effect  of  echo  ;  but  the 
true  cause  probably  is,  that  the  sound  is  developed  by 
the  lightning  in  passing  through  the  air,  and  conse- 
quently separate  sounds  are  produced  at  every  point 
through  which  the  lightning  passes. 

187*5   Why  is  thunder  sometimes  one  vast  crash? 

Because  the  lightning  cloud  is  near  the  earth  ;  and 
as  all  the  vibrations  of  the  air  (on  which  sound  depends) 
reach  the  ear  at  the  same  moment,  they  seem  like  one 
vast  sound. 

187*0  Why  is  the  thunder  generally  heard  several  moments  after  the 
/lash? 

Because  it  has  a  long  distance  to  travel.  Lightning 
travels  nearly  a  million  times  faster  than  thunder ;  if, 
therefore,  the  thunder  has  a  great  distance  to  come,  it 
will  not  reach  the  earth  till  a  considerable  time  after 
the  flash. 

187"?  Can  we  not  tell  the  distance  of  a  thunder  cloud  by  observing  the 
interval  which  elapses  betiveen  the  flash  and  the  peal  f 

Yes ;  the  flash  is  instantaneous,  but  the  thunder  will 
take  a  whole  second  of  time  to  travel  three  hundred  and 
eighty  yards  ;  hence,  if  the  flash  be  five  seconds  before 
thunder,  the  cloud  is  nineteen  hundred  yards  off. 

i.  e.  380  x  5=1900  yards. 

187*8    What  is  the  aurora  borealis  or  northern  lights  f 

JLuminous  appearances  seen  in  the  sky  at  night-time. 
Sometimes  streaks  of  blue,  purple,  green,  red,  etc.,  and 
sometimes  flashes  of  light,  are  seen. 

187*9    What  is  the  cause  of  the  aurora  borealis  or  northern  lights  ? 

Electricity  in  the  higher  regions  of  the  atmosphere 
is  undoubtedly  an  active  agent  in  producing  this  pheno- 
menon. 

188O  Is  the  aurora  ever  seen  in  other  parts  of  the  heavens  than  towards 
the  north  f 

In  the  northern  hemisphere  it  always  appears  in  the 


288 


SCIENCE   OF   COMMON    THINGS. 


Extent  of  the  aurora.  Height  of  the  aurora.  Appearance. 


north)  but  in  the  southern  hemisphere  it  appears  in  the 
south :  it  seems  to  originate  at  or  near  the  poles  of  the 
earth,  and  is  consequently  seen  in  its  greatest  perfection 
within,  the  arctic  and  antarctic  circles. 

1S81    What  is  known  concerning  the  extent  of  the  auroral 

It  is  not  local,  but  it  is  seen  simultaneously  at  places 
widely  remote  from  each  other,  as  in  Europe  and 
America. 

1883  What  calculations  "have  been  made  respecting  the  height  of  the 
aurora  f 

The  height  of  the  appearances  varies  from  one  to  two 
hundred  miles /  they  sometimes  appear  within  the 
region  of  the  clouds,  and  very  near  to  the  earth. 

1883  Do  the  auroras  appear  at  any  particular  seasons  and  times  f 

They  appear  more  frequently  in  the  winter  than  in 
the  summer,  and  are  only  seen  at  night. 


Fig.  84. 


The  accompanying  figure  represents  one  of  the  most  beautiful  of  the 
auroral  phenomena. 

1884  Do  they  also  occur  in  the  day -time  f 

The  aurora  is  known  to  affect  the  magnetic  needle  and 


SCIENCE   OF   COMMON   THINGS. 


Aurora-borealis  occurs  In  the  day-time.  TThat  is  galvanism  ? 


the  telegraph ;  and  as  the  effects  upon  these  instruments 
are  noticed  by  day  as  well  as  by  night,  there  can  be  no 
doubt  of  the  occurrence  of  the  aurora  at  all  hours.  The 
intense  light  of  the  sun  renders  the  auroral  light  in- 
visible during  the  day. 

1385   Of  what  utility  are  the  auroral  appearances  in  the  polar  regions  ? 

During  the  long  polar  night,  when  the  sun  is  absent, 
the  aurora  appears  with  a  magnificence  unknown  in 
other  regions,  and  affords  light  sufficient  for  many  of 
the  ordinary  out-door  employments. 


CIIAPTEE   II. 

GALVANISM. 

1886    What  is  galvanism  ? 

It  is  the  production  of  electrical  disturbance  by  chemi- 
cal action. 

1887*  What  is  the  most  simple  manner  of  illustrating  the  production  of 
this  electricity? 

If  we  place  a  piece  of  silver  on  the  tongue,  and  a 
piece  of  zinc  underneath  it,  no  effect  will  be  produced 
as  long  as  the  two  metals  are  kept  asunder ;  but  when 
their  ends  are  brought  together,  a  distinct  thrill  will 
pass  through  the  tongue,  a  metallic  taste  will  diffuse 
itself,  and,  if  the  eyes  are  closed,  a  sensation  of  light 
will  be  evident  at  the  same  moment. 

1888  To  what  is  this  result  owing  f 

To  a  chemical  action  developed  the  moment  the  two 
metals  touched  each  other. 

The  saliva  of  the  tongue  oxidizes  a  portion  of  the  zmc,  which  excites 
electricity,  for  no  chemical  action  ever  takes  place  without  producing  elec- 
tricity. Upon  bringing  the  ends  of  the  two  metals  together,  a  slight 
current  passes  from  one  to  the  other. 

1889  By  whom  was  the  production  of  galvanic  electricity  first  noticed  t 


290 


SCIENCE   OF   COMMON   THINGS. 


How  galvanic  electricity  was  discovered. 


By  Galvani,  professor  of  anatomy  at  Bologna,  Italy, 
in  1790. 

Having  occasion  to  dissect  several  frogs,  he  hung  up  their  hind  legs  on 
some  copper  hooks,  until  he  might  find^t  necessary  to  use  them  for  illus- 
tration. In  this  manner  he  happened  to  suspend  a  number  of  the  copper 
hooks  on  an  iron  balcony,  when,  to  his  great  astonishment,  the  limbs  wero 
thrown  into  violent  convulsions. 

189O   On  investigating  the  phenomena  what  did  Galvani  discover  ? 

He  found  that  whenever  the  nerves  of  a  frog's  leg 
were  touched  by  one  metal  and  the  muscles  by  another, 
convulsions  took  place  on  bringing  the  two  different 
metals  in  contact. 


Fig.  85. 

This  is  explained  by  reference  to  Fig.  85,  which  represents  a  frog's  legs, 
the  upper  part  dissected  in  such  a  way  as  to  exhibit  the  nerves  of  the  legs-?., 
and  a  portion  of  the  spinal  marrow.  If  we  now  take  two  thin  pieces  of  cop- 
per and  zinc.  C  z,  and  place  one  under  the  nerves,  and  the  other  in  contact 
with  the  muscles  of  the  leg,  we  shall  find  that  so  long  as  the  two  pieces 
of  metal  are  separated,  so  long  will  the  limbs  remain  motionless,  but  by 
making  a  connection,  instantly  the  whole  lower  extremities  will  be  thrown 
into  violent  convulsions,  quivering  and  stretching  themselves  in  a  manner 
too  singular  to  describe.  If  the  wire  is  kept  closely  in  contact,  these 
phenomena  are  of  momentary  duration,  but  are  renewed  every  time  the 


SCIENCE   OF  COMMON   THINGS. 


291 


Construction  of  a  galvanic  battery. 


Origin  of  the  term  "galvanism.'' 


Fig.  86. 


contact  is  made  and  broken,     Here,  then,  we  have  distinct  evidence  of 
the  presence  of  free  electricity,  developed  apparently  by  simple  contact. 

1891  What  is  the  simplest  way  of  exciting  a  current  of  galvanic  elec- 
tricity f 

By  arranging  a  series  of  metal  plates  in  a 
pile,  placing  them  in  pairs,  with  a  wet  cloth 
Between  them,  it  berng  necessary  that  one 
of  each  pair  should  be  more  easily  oxidized 
than  the  other.  The  simple  contact  of  these 
plates  will  produce  a  feeble  and  continued 
galvanic  current. 

Fig.  86  represents  an  arrangement  of  this  character. 

180S  What  is  such  an  arrangement  of  plates  for  pro- 
ducing electrical  currents  called  f 

A  galvanic  or  voltaic  battery. 

1893  Why  are  the  terms  "galvanic"  and  "voltaic" 
applied  ? 

They  originated  in  honor  of  Galvani  and 
Volta,  the  Italian  philosophers  who  first  de- 
veloped these  phenomena  of  chemical  electricity,  and 
the  means  of  producing  them. 

1894  Are  there  many  metals  or  other  substances  which,  wlien  brought 
together,  are  capable  of  producing  galvanic  action  f 

The  number  is  quite  large ;  among  them  we  may 
enumerate  the  following :  zinc,  lead,  tin,  antimony, 
iron,  brass,  copper,  silver,  gold,  platinum,  Hack  lead  or 
graphite,  and  charcoal. 

1895  Witt  any  two  of  these  brought  together  produce  a  galvanic  current  f 

They  will :  but  they  possess  the  power  in  different 
degrees  ;  and  the  more  remote  they  stand  from  each 
other  in  the  order  above  given,  the  more  decidedly  will 
the  chemical  electricity  be  developed. 

Thus  zinc  and  lead  will  produce  a  voltaic  battery,  but  it  will  be  much 
less  active  than  zinc  and  iron,  or  the  same  metal  and  copper,  and  this  last 
less  active  than  zinc  and  platinum,  or  zinc  and  charcoal. 

1896  Does  galvanic  or  voltaic  electricity  appear  to  consist  of  two  kinds, 
positive  and  negative,  as  in  ordinary  electricity  ? 

It  does ;  positive  electricity  always  flows  from  tlie 
'metal  which  is  acted  upon  most  powerfully,  and  nega- 
tive electricity  from  the  other. 


292 


SCIENCE   OF   COMMON   THINGS. 


Poles  of  a  battery.    Means  by  which  galvanic-electricity  in  quantity  can  be  developed. 
1897*   What  do  we  mean  when  we  speak  of  a  galvanic  circuit  ? 

The  connection  of  the  two  metals  in  the  battery,  so 
that  the  positive  and  negative  electricities  can  meet, 
and  flow  in  opposite  directions. 

1898  At  what  point  in  the  circuit  will  the  manifestations  of  electricity 
be  most  apparenl  ? 

At  the  point  where  the  two  currents  meet. 

'     1899   What  is  meant  by  the  poles  of  the  battery  ? 

The  two  metals  forming  the  elements  of  the  battery 
are  generally  connected  by  copper  wires ;  the  ends  of 
these  wires,  or  the  terminal  points  of  any  other  connect- 
ing medium  used,  are  called  the  poles  of  the  battery. 

Thus,  when  zinc  and  copper  poles  are  used,  the  end  of  the  wire  con- 
veying positive  electricity  from  the  zinc  would  be  the  pbsitive  pole,  and 
the  end  of  the  wire  conveying  negative  electricity  from  the  copper  plate 
would  be  the  negative  pole.  Faraday  describes  the  poles  of  the  battery 
as  the  doors  by  which  electricity  enters  into  or  passes  out  of  the  substance 
suffering  decomposition. 

A  very  simple,  and  at  the  same  time  an  active,  galvanic  circuit  may  be 
formed  by  an  arrangement  as  re- 
presented in  Fig.  87.  C  and  Z  are 
thin  plates  of  copper  and  zinc  im- 
mersed in  a  glass  vessel  containing 
a  very  weak  solution  of  sulphuric 
acid  and  water.  Metallic  contact 
is  made  by  means  of  the"  wires,  X 
and  W,  soldered  to  the  plates,  the 
poles  intersecting  at  Y.  The  cur- 
rent of  positive  electricity,  when 
the  circuit  is  closed,  passes  from 
the  zinc,  through  the  liquid,  to  the 
copper,  and  from  the  copper,  along 
the  conducting  wires,  to  the  zinc, 
as  indicated  by  the  arrows  in  the 
figure.  A  current  of  negative  elec- 
tricity traverses  the  circuit  also,  Fig.  87. 
from  the  copper  to  the  zinc,  in  a 
direction  precisely  reversed. 

1900  By  lohat  chemical  action  can  the  greatest  abundance  of  galvanic 
electricity  be  developed  ? 

By  the  oxidation  of  metallic  zinc  by  weak  sulphuric 
acid. 

01 Ol  The  electricity  developed  by  the  action  of  a  single  pair  of  plates 
immersed  in  acid  water  is  very  feeble :  how  can  it  be  increased  ? 

By  increasing  the  number  of  the  plates  and  the  quan- 


SCIENCE   OF   COMMON   THINGS 


293 


Different  forms  of  galvanic  batteries.  Light  and  beat  produced  by  galvanism. 

tity  of  the  liquid,  we  increase  the  intensity  of  the  elec- 
tricity developed. 


Fig.  88. 


Fig.  89. 


Figs.  88  and  80  represent  some  of  the  most  common  forms  of  galvanic 
batteries.  In  Fig.  88  two  plates  of  zinc,  z  z,  inclosing  a  piece  of  silver 
between  them,  are  immersed  in  a  glass  cylinder,  Gr,  containing  acid ;  S 
and  A  represent  the  poles  of  the  battery.  In  Fig.  89  the  battery  con- 
gists  of  two  concentric  cups  or  cylinders  of  copper,  C,  and  a  cylinder  of 
zinc,  Z,  fitting  between.  The  acid  solution  is  poured  into  the  spaces  be- 
tween the  cylinders.  Another  form  consists  of  an  earthenware  trough, 
containing  acid,  in  which  alternate  plates  of  copper  and  zinc  are  arranged, 
and  connected  together  by  wires  rising  from  each  end  of  the  trough. 

19O3  What  are  the  most  ordinary  effects  produced  by  the  developed 
electricity  of  a  large  galvanic  battery  f 

The  production  of  sparks  and  brilliant  flashes  of 
light,  the  heating  and  fusing  of  metals,  the  deflagration 
of  gunpowder  and  other  inflammable  substances,  and 
the  decomposition  of  water,  saline  compounds,  and 
metallic  oxides. 

19  O3  How  may  the  most  splendid  artificial  light  known  be  produced  f 

By  fixing  pieces  of  pointed  charcoal  to  the  wires 
connected  with  opposite  poles  of  a  powerful  galvanic 
battery,  and  bringing  them  into  contact. 

19  O  4  Can  intense  heat  be  developed  by  the  action  of  the  galvanic  bat- 
tery as  well  as  intense  light  ? 

The  greatest  artificial  heat  man  has  yet  succeeded  in 
producing  has  been  through  the  agency  of  the  galvanic 
oattery. 

19O5    What  refractory  substances  c&n  be  fused  by  the  aid  of  the  gal' 

vanic  battery  f 

All  the  metals,  including  platinum,  can  be  readily 


294  SCIENCE   OF   COMMON   THINGS. 

Principles  and  processes  of  electro-metallurgy. 

melted  /  quartz,  sulphur,  magnesia,  slate,  and  lime  are 
liquefied ;  and  the  diamond  fuses,  boils,  and  becomes 
converted  into  coal. 

19 OG   What  is  ekctrotyping,  or  electro-metallurgy  ? 

It  is  the  art  or  process  of  depositing,  from  a  metallic 
solution,  through  the  agency  of  galvanic  electricity,  a 
coating  or  film  of  metal  upon  some  other  substance. 

19O7   Upon  what  principles  is  it  accomplished  f 

The  process  is  based  on  the  fact,  that  when  a  galva- 
nic current  is  passed  through  a  solution  of  some  metal, 
as  a  solution  of  sulphate  of  copper  (sulphuric  acid  and 
copper),  decomposition  takes  place  /  the  metal  is  sepa- 
rated in  a  metallic  state,  and  attaches  itself  to  the  nega- 
tive pole,  or  to  any  substance  that  may  be  attached  to 
the  negative  pole;  while  the  acid  or  other  substance 
before  in  combination  with  the  metal,  goes  to,  and  is 
deposited  on  the  positive  pole. 

In  this  way  a  medal,  a  wood-engraving,  or  a  plaster  cast,  if  attached 
to  the  negative  pole,  may  be  covered  with  a  coating  of  copper;  if  the 
solution  had  been  one  containing  silver  or  gold,  the  substance  would 
have  been  covered  with  a  coating  of  silver  or  gold  instead  of  copper. 

19  OS  How  can  the  thickness  of  the  deposits  be  regulated  f 

The  thickness  of  the  deposit,  providing  the  supply 
of  the  metallic  solution  be  kept  constant,  will  depend 
on  the  length  of  time  the  object  is  exposed  to  the  influ- 
ence of  the  'battery. 

In  this  way,  a  coating  of  gold  thinner  than  the  thinnest  gold-leaf  can 
be  laid  on,  or  it  may  be  made  several  inches  or  feet  in  thickness,  if 
desired. 

The  process  of  electrotyping  has  been  strikingly  taken  advantage  of  in 
reproducing  expensive  engraved  plates,  as  the  map-plates  of  the  Coast 
Survey  of  the  United  States.  The  plate  of  the  map,  usually  on  copper,  is 
frequently  the  work  of  years  under  the  hand  of  the  engraver,  the  cost 
being  counted  by  thousands  of  dollars.  If  the  plate,  when  finished,  were 
printed  on  directly,  the  pressure  of  the  paper  a  few  hundred  times  would 
goon  obliterate  the  faint  lines  of  the  engraving  on  the  metal,  and  the  plate 
would  soon  become  injured  or  spoiled.  But  now  the  original  plate  is 
uever  printed  on.  but  an  electrotype  on  copper  is  taken  from  it,  at  a  very 
email  expense  ;  and  this  may  be  repeated  almost  indefinitely,  thus  afford- 
mg  fresh  plates  for  printing  whenever  required. 


SCIENCE   OF   COMMON   THINGS.  295 

Magnetism.  Natural  magnets.  Where  found. 

CHAPTER   III 

MAGNETISM. 

1909  Is  there  any  connection  "between  magnetism  and  electricity  f 

There  is  every  reason  to  believe  that  magnetism  and 
electricity  are  but  modifications  of  one  force. 

10 1O  What  is  a  loadstone  or  a  natural  magnet  f- 

It  is  an  ore  of  iron,  known  as  the  "protoxide  of 
iron"  or  " magnetic  oxide  of  iron"  which  is  capable 
of  attracting  other  pieces  of  iron  to  itself;  and  if  sus- 
pended freely  by  a  thread,  and  left  to  take  its  own  po- 
sition, it  will  arrange  itself  so  that  its  extremities  will 
point  towards  the  north  and  south,  poles  of  the  earth. 

1911  Are  natural  magnets  rare  ? 

They  are  not  •  they  are  found  in  many  places  in  the 
United  States.  In  Arkansas,  especially,  an  ore  of  iron 
possessing  remarkably  strong  attractive  powers  is  very 
abundant. 

The  magnetic  ore  is  usually  of  a  dark 
grey  hue,  and  possesses  but  little  me- 
tallic lustre.  Fig.  91.  If  a  piece  of  this 
ore  be  dipped  in  iron  filings,  or  a  number 
of  small  needles,  they  will  generally  be 
found  collected  and  clinging  together  in 
great  quantities  at  two  opposite  extremi- 
ties, as  represented  in  the  figure,  whilst 
the  middle  portion  is  nearly  destitute. 
The  magnetic  property,  whatever  it  may  F5B.  91. 

be,  seems  therefore  to  be  collected  and  act 
with  the  greatest  energy  at  two  opposite  extremes;  these  have  been 
termed  poles. 

1913    What  is  the  origin  of  the  terms  "  magnet"  and  "  magnetism  ?" 

The  loadstone  or  natural  magnet  was  first  found  at 
Magnesia,  in  Lydia,  Asia,  whence  were  derived  the 
names. 

1913  Can  a  natural  magnet  communicate  its  attractive  properties  to 
sther  bodies  by  contact  ? 

It  can,  and  that  too  without  any  apparent  loss  of 
attractive  strength. 


296  SCIENCE   OF   COMMON   THINGS. 

Bodies  capable  of  being  magnetized.  Induction.  Magnetic  needle. 

1014  What  bodies  are  capable  of  being  magnetized  by  contact  with 
natural  magnets  ? 

Iron  and  steel  are  the  substances  most  susceptible  of 
tins  influence,  but  brass,  nickel,  and  cobalt  can  also 
become  magnets. 

1015  Does  the  magnetism  imparted  to  a  piece  of  soft  iron,  or  steel,  by 
contact  with  a  natural  magnet,  remain  permanent  in  their  substances  f 

In  the  steel  it  does^  but  the  soft  iron  loses  its  power  as 
soon  as  it  is  removed  from  the  magnet. 

1016  Is  it  necessary  that  absolute  contact  should  take. place  between  a 
magnet  and  a  pwcu  of  soft  iron  to  render  the  latter  a  magnet  1 

No,  every  piece  of  soft  iron  brought  near  a  magnet 
becomes  by  induction  itself  a  magnet. 

IS*!*?   What  dc  you  mean  by  induction  ? 

It  is  the  production  of  like  effects  in  contiguous  bo- 
iifs.  In  electricity  or  magnetism,  it  is  the  influence 
exerted  by  an  electrified  or  magnetized  body  through 
a  non-conducting  medium  without  any  apparent  com- 
munication of  a  current. 

1018   What  is  meant  by  the  directive  power  of  the  magnet  f 

It  is  that  power  which  will  cause  a  magnet,  when 
suspended  freely,  to  constantly  turn  the  same  part  to- 
wards the  north  pole  and  the  opposite  part  towards  the 
south  pole  of  the  earth. 

1010    What  are  the  poles  of  a  magnet  f 

They  are  the  ends  of  the  magnet,  and  are  denomi- 
nated north  and  south  poles,  according  as  they  point  to 
the  north  or  south  poles  of  the  earth. 

103O   What  are  the  poles  of  the  earth  ? 

The  extremities  of  the  earths  axis,  or  the  points  on 
the  surface  of  the  globe  through  which  the  axis  passes. 

1031    What  is  a  magnetic  needle  ? 

Simply  a  bar  of  steel  which  is  a 
magnet,  suspended  in  such  a  way 
that  it  can  freely  turn  to  the  north 
or  south. 

1033    What  is  a  mariner's  compass  f 

It   is   a   delicate    steel    lar    or 

Jig.  92- 


SCIENCE   OF   COMMON   THINGS.  297 

The  magnetic  compass.  ^Discovery  and  first  use  of  the  compass. 

needle  balanced  upon  &  pivot  placed  beneath  its  centre 
of  gravity  in  such  a  way  that  it  can  turn  horizontally 
without  obstruction.  This  needle  is  usually  inclosed  in 
a  box,  upon  the  bottom  of  which  is  a  card,  with  the 
various  points- — north,  south,  east,  west,  etc.,  etc., 
marked  upon  it. 


Fig-  92. 

Such  a  needle,  if  the  box  containing  it  be- placed  on  a  level  surface,  will 
generally  be  observed  to  vibrate  more  or  less,  till  it  settles  in  such  a 
direction  that  one  of  its  extremities  or  poles  will  point  towards  the  north, 
and  the  other  consequently  towards  the  south.  If  the  position  of  the  box 
be  altered  or  reversed,  the  needle  will  always  turn  and  vibrate  again,  till 
its  poles  have  attained  the  same  direction  as  before. 

1933  Does  the  compass  needle  always  point  exactly  north  and  south  ? 

It  does  not  /  its  natural  direction  is  towards  the  north 
and  south  poles,  but  it  seldom  points  due  north  or 

south. 

1934  Who  first  discovered  the  fact  that  a  magnet  would  invariably 
point  to  the  north  -and  the  south,  and  made  use  of  this  knowledge  in  construct- 
ing a  ompass? 

It  is  claimed  to  have  been  discovered  by  the  Chinese: 
it  was  known  in  Europe,  and  used  in  the  Mediterranean, 
in  the  thirteenth  century. 

1935  How  were  the  compasses  of  that  time  constructed? 

They  were  merely  pieces  of  loadstone  fixed  to  a  cork, 
which  floated  on  the  surface  of  water. 

1936  Is  the  earth  itself  supposed  to  be  a  magnet? 

It  is  undoubtedly  a  great  magnet. 


208  SCIENCE    OF   COMMON   THINGS 

How  iron  bars  become  magnetic.  Horse-shoe  magnets. 

1937  Is  iron  under  certain  circumstances  rendered  magnetic  by  the 
inductive  action  of  tlie  earth} s  magnetism  f 

Most  iron  bars  and  rails,  as  the  vertical  bars  of  win- 
dows, that  have  stood  for  a  considerable  time  in  a  per- 
pendicular position,  will  be  found  to  be  magnetic. 

1938  If  we  suspend  a  bar  of  soft  iron  sufficiently  long  in  the  air,  will  it 
assume  magnetic  properties  ? 

It  will  gradually  become  magnetic;  and  although 
5vlien  it  is  first  suspended  it  points  indifferently  in  any 
direction,  it  will  at  last  point  north  and  south. 

1939  How  may  a  bar  of  iron,  such  as  a  kitchen  poker,  be  made  imme- 
diately magnetic,  without  resorting  to  the  use  of  other  magnets  f 

If  the  bar  devoid  of  magnetism  is  placed  with  one 
end  on  the  ground,  slightly  inclined  towards  the  north, 
and  then  struck  one  smart  blow  with  a  hammer  upon 
the  upper  end,  it  will  immediately  acquire  polarity,  and 
exhibit  the  attractive  and  repellant  Droperties  of  a 
magnet. 

1930  What  is  a  horse-shoe  magnet  f 

It  is  a  magnetic  bar  bent  into  the  form  of  a  horse-shoe. 

"When  a  piece  of  iron  not  magnetic  is  brought  in 
contact  with  a  common  magnet,  it  will  be  attracted 
by  either  pole;  but  the  most  powerful  attraction 
takes  place  when  both  poles  can  be  applied  to  the 
surface  of  the  piece  of  iron  at  once.  The  magnetic 
bars  are  for  this  purpose  bent  into  the  shape  of  the 
letter  U,  and  are  termed  horse-shoe  magnets. 
Several  of  these  are  frequently  joined  together 
with  their  similar  poles  in  contact ;  they  then  con- 
stitute a  magnetic  battery,  and  are  very  powerful, 
either  for  lifting  weights,  or  charging  other  mag- 
Fig.  93.  nets.  (See  Fig.  93.) 

1931  If  we  break  a  magnet  across  the  middle,  what  happens  f 

Each  fragment  becomes  converted  into  a  perfect 
magnet;  the  part  which  originally  had  a  north  pole 
acquires  a  south  pole  at  the  fractured  end,  and  the  part 
which  originally  had  a  south  pole,  gets  a  north  pole. 

1933  If  we  divide  up  a  magnet  to  the  extreme  degree  of mechanical  fine- 
ness possible,  will  the  pieces  possess  magnetic  powers  f 

Each  fragment,  however  small,  will  be  a  perfect 
magnet 


SCIENCE   OF   COMMON   THINGS.  299 

Electro-magnetism.  When  and  how  discovered. 

CHAPTER   IY. 

ELECTRO-MAGNETISM. 
1933    What  is  electro-magnetism  f 

It  is  the  magnetism  developed  through  the  agency 
of  electrical  or  galvanic  action. 

1034  What  were  the  earliest  phenomena  observed  which  indicated  a 
relation  between  magnetism  and  electricity  f 

It  was  noticed  that  ship's  compasses  have  their  direc- 
tive power  impaired  by  lightning,  and  that  sewing 
needles  could  be  rendered  magnetic  by  electric  dis- 
charges passed  through  them. 

1935  What  discovery,  made  by  Prof.  Oersted  of  Copenhagen,  esta- 
blished beyond  a  doubt  the  connection  of  electricity  and  magnetism  f 

He  ascertained  that  a  magnetic  needle  placed  near  a 
metallic  wire  connecting  the  poles  of  a  galvanic  battery 
was  compelled  to  change  its  direction,  and  that  the  new 

direction  it  assumed  was  deter- 
mined by  its  position  in  rela- 
tion to  the  wire  and  to  the  di- 
rection of  the  current  trans- 
mitted along  the  wire. 

Thus,  if,  as  in  Fig.  94,  a  needle  be  in- 
Fig.  94.  closed  in  a  wire  not  touching  it  at  any 

point,  and  a  current  of  electricity  pass 

through  the  wire,  the  needle  will  be  made  to  move  in  accordance  with  the 
direction  of  the  current 

1036  What  other  important  discovery  was  made  about  the  same 
time  ? 

It  was  found  that  if  a  piece  of  soft  iron,  not  possessing 
magnetic  power  sufficient  to  elevate  a  grain  weight,  be 
placed  within  a  coil  of  copper  wire  through  which  a 
galvanic  current  is  passing,  it  will  become,  through  the 
influence  of  the  current,  a  powerful  magnet ;  and  will, 
so  long  as  the  current  flows,  sustain  weights  amount- 
ing to  many  hundreds  of  pounds.  (See  figs.  95  and 
96.) 


300 


SCIENCE    OP   COMMON   THINGS. 


Excitation  of  Magnetism.  Morse's  Magnetic  Telegraph. 


Fig.  94. 


Fig.  95. 


193*7  Is  Hie  magnetic  power  of  the  bar  found  to  be  wholly  dependent  on 
(he  existence  of  the  current  f 

It  is  /  the  moment  the  current  stops,  the  weights 
fall  away  from  the  bar  in  obedience  to  the  law  of 
gravity. 

1933  How  great  weights  have  been  lifted  by  magnets  formed  in  this 
manner  1 

An  electro-magnet  constructed  by  Prof.  Henry  was 
capable  of  elevating  and  sustaining  about  a  ton  weight. 

1939  Upon  what  principle  does  the  construction  of  the  Morse  magnetic 
telegraph  depend  ?. 

Upon  the  principle  that  a  current  of  electricity  circu- 
lating about  a  bar  of  soft  iron  is  capable  of  rendering  it 
a  magnet. 

The  arrangement  by  which  this  principle  is  made  available  in  the  con- 
struction and  operation  of  the  Morse  magnetic  telegraph  will  be  under- 
stood by  reference  to  the  accompanying  diagram  (Fig.  96),  which  repre- 
sents the  construction  and  arrangement  of  this  form  of  telegraph.  F  and 
E  are  pieces  of  soft  iron  surrounded  by  coils  of  wire,  which  are  connected 
at  o  and  b  with  wires  proceeding  from  a  galvanic  battery.  When  a  cur- 
rent is  transmitted  from  a  battery  located  one,  two,  or  three  hundred 
miles,  as  the  case  may  be,  it  passes  along  the  wires  and  into  the  coils  sur- 
rounding the  pieces  of  soft  iron  F  and  E,  thereby  converting  them  into 
magnets.  Above  these  pieces  of  soft  iron  is  a  metallic  bar  or  lever,  A, 
supported  on  its  centre,  and  having  at  one  end  the  arm  D,  and  at  the 
other  a  small  steel  point,  o.  A  ribbon  of  paper,  p  h,  rolled  on  the  cylinder 
B,  is  drawn  slowly  and  steadily  off  by  a  train  of  clock-work,  K,  moved  by 
the  action  of  the  weight  P  on  the  cord  C.  This  clock-work  gives  motion 
to  two  metal  rollers,  G  and  H,  between  which  the  ribbon  of  paper  passes, 
and  which,  turning  in  opposite  directions,  draw  the  paper  from  the  cylin- 
der B.  The  roller  H  has  a  groove  around  its  circumference  (not  repre- 
sented in  the  engraving)  above  which  the  paper  passes.  The  steel  point, 
9,  of  the  lever,  A,  is  also  directly  opposite  this  groove.  The  spring  r  pre- 


SCIENCE   OF   COMMON   THINGS. 


301 


Telegraph,  magnetic,  principles  of. 


Intelligence,  how  conveyed  by. 


Fig.  96. 

vents  the  point  from  resting  upon  the  paper  when  the  telegraph  is  not  in 
operation. 

1940  Why  is  it  necessary,  in  conveying  the  telegraph  wires,  to  support 
them  upon  glass  or  earthen  cylinders  f 

These  are  used  for  the  purpose  of  insuring  the  perfect 
insulation  of  the  wires,  since  but  for  this  the  electricity 
would  pass  down  a  damp  pole  to  the  earth,  and  be  lost. 

1941  Is  there  any  truth  in  the  idea  that  many  persons  have,  that  some 
principle  passes  along  the  telegraphic  wires  when  intelligence  is  transmitted  ~? 

This  supposition  is  wholly  erroneous  ;  the  word  cur- 
rent, as  something  flowing,  conveys  a  false  idea,  but  we 
have  no  other  term  to  express  electrical  progression. 

1943  How  can  we,  gain  an  idea  of  what  really  takes  place,  and  of  the 
nature  of  the  influence  transmitted  ? 

The  earth  and  all  matter  are  reservoirs  of  electricity  ; 
if  we  disturb  this  electricity  at  Boston  by  voltaic  influ- 
ence, its  pulsations  may  be  felt  in  New  York.  Suppose 
the  telegraphic  wire  were  a  tube,  extending  from 
Boston  to  New  York,  filled  with  water.  Now,  if  one 
drop  more  is  forced  into  it  at  Boston,  a  drop  must  fall 
out  at  New  York,  but  no  drop  was  caused  to  pass  from 
Boston  to  New  York.  Something  similar  to  this  occurs 
in  the  transmission  of  electricity. 


302  SCIENCE   OF   COMMON   THINGS. 

"What  is  starch  ?  How  manufactured  ? 

PART  IX. 

FAMILIAR  CHEMISTRY. 


1943  What  is  starch  f 

The  name  starch  is  given  to  a  mealy  substance  which 
is  deposited  in  most  vegetables  at  the  time  of  ripening, 
from  the  juices  with  which  the  cells  of  the  plants  are 
filled. 

1944  What  common  vegetable  especially  abounds  in  starch  f 

The  potato  ;  which  consists  entirely  of  cells  filled 
with  starch  and  water. 

A  cell  is  a  little  membranous  bladder  filled  with  a  solid  or  fluid  sub- 
stance. 

1945  Why  does  the  laundress  find  it  necessary  to  boil  starch  before 
using  it  for  stiffening  linen,  etc.  f 

The  starch,  consisting  of  little  granules,  is  insoluble 
in  cold  water ;  but  when  acted  upon  by  hot  water, 
the  granules  burst  and  allow  their  contents,  which  are 
soluble,  to  become  mingled  with  the  water. 

Starch  is  manufactured  as  follows : — 

Potatoes,  for  example,  from  which  most  of  the  starch  of  commerce  is 
manufactured,  after  being  pared,  are  grated  to  a  pulp.  This  pulp  is  put 
upon  a  sieve  and  stirred  about,  while  at  the  same  time  a  little  stream  of 
water  is  made  to  flow  upon  it.  A  milkjr  liquid  runs  through  the  sieve, 
but  the  fibrous  portion  of  the  potato,  the  vegetable  tissue,  remains  behind. 
This  liquid,  after  a  short  interval,  deposits  a  white  powder,  which  is  the 
starch.  By  the  simple  process  of  tearing  up  the  vegetable  tissue,  and 
removing  the  inclosed  starch  by  washing,  this  substance  may  be  procured 
from  a  great  variety  of  plants. 

1946  Why  do  potatoes,  beans,  rice,  and  most  of  the  common  vegetables, 
swell  up  when  boiled  with  water  f 

Because  the  starch  absorbs  water  at  the  boiling  tern- 


SCIENCE    OF   COMMON   THINGS.  303 


Composition  of  wheat  flour.  Acids.  Alkalies. 


perature,  which  causes  the  cells  to  swell,  thereby  giv- 
ing to  the  vegetable  a  rounded  appearance. 

1947*    What  is  the  composition  of  wheat  flour? 

Starch  is  one  of  the  principal  constituents  of  wheat 
flour,  as  well  as  of  all  other  kinds  of  meal.  The  other 
principal  constituent  is  a  grey,  tough,  viscous  sub- 
stance, called  gluten. 

1048  To  what  does  paste,  made  of  wheat  or  rye  flour,  owe  its  adhe~ 
siveness  f 

In  some  measure  to  the  starch,  but  principally  to  the 
gluten  contained  in  it. 

1949  Can  starch  be  converted  into  gum.  and  sugar  f 

It  can  ;  fruits  and  plants  effect  this  change  natu- 
rally:  we  can  also  produce  the  change  artificially  by 
chemical  *  rocesses. 

50 SO  Why  are  potatoes  frozen  and  thawed  sweet  f 

Because  by  the  freezing  action  the  starch  of  the  po- 
tato is  in  part  converted  into  sugar. 

1951  Why  are  apples,  pears,  grapes,  etc.,  in  their  unripe  state  sour, 
and  in  their  ripe  condition  sweet  ? 

In  the  unripe  fruits  mentioned  starch  is  present ;  in 
the  ripe  fruits  it  is  absent  •  in  the  process  of  ripening 
the  starch  is  converted  into  sugar,  and  the  fruit  losing 
its  sour  taste,  becomes  sweet. 

1953    What  are  acids  f 

Acids  are  substances  which  excite  the  taste  of  sour- 
ness when  applied  to  the  tongue  ;  they  change  the  blue 
juices  of  vegetables  to  red,  and  combine  with  alkalies 
to  form  neutral  compounds. 

1953    What  is  an  alkali? 

An  alkali  is  a  body  that  possesses  properties  the 
converse  of  those  of  an  acid.  It  has  a  highly  bitter, 
acrid  taste,  changes  the  blue  juices  of  vegetables  green, 
or  the  juices  of  vegetables  which  have  been  changed 
red  by  an  acid,  back  again  to  blue.  Potash  and  soda 
are  the  representatives  of  the  alkalies. 

3.954    When  sulphur  is  burned  in  the  air  what  is  the  product  formed  1 

Sulphurous  acid. 


304:  SCIENCE   OF   COMMON   THINGS. 

Sulphuric,  nitric,  and  muriatic  acids.  Sulphuretted  hydrogen. 


1955  What  causes  the  suffocating  odor  of  a  lighted  brimstone  match  ? 

The  sulphurous  acid  generated  by  the  combustion 
of  the  sulphur. 

1956  What  is  sulphuric  acid  or  oil  of  vitriol  r 

It  is  a  compound  of  sulphur  and  oxygen,  containing 
one-third  more  oxygen  than  sulphurous  acid. 

1057    What  is  sulphuretted  hydrogen  f 

,     A  gas  formed  by  the  union  of  sulphur  and  hydrogen. 
llt  possesses  an  offensive  odor,  and  is  very  poisonous. 

1953  How  is  sulphuretted  hydrogen  formed  in  nature  f 

Principally  from  the  decomposition  of  animal  $ub~ 
stances,  as  blood,  flesh,  hair,  etc. 

1959  Why  does  the  yolk  of  an  egg  tarnish  a  silver  spoon  ? 

Because  it  contains  a  little  sulphur,  which,  at  the 
temperature  of  an  egg  just  boiled,  will  decompose  the 
water  or  moisture  upon  the  spoon,  and  produce  sul- 
phuretted hydrogen  gas,  which  will  tarnish  silver. 

Both  the  white  and  the  yolk  contain  sulphur,  but  the  latter  the  most 
abundantly. 

1960  What  is  it  that  makes  an  open  or  foul  sewer  so  destructive  of 
health  to  any  district  in  which  it  may  be  situated  ? 

The  evolution  of  sulphuretted  hydrogen.  When  in- 
haled, it  acts  directly  upon  the  blood,  thickening  it, 
and  turning  it  black. 

1961  Why  do  surfaces  painted  with  lead  paints,  in  the  vicinity  of  sew- 
ers, soon  turn  black,  or  become  discolored  f 

Through  the  action  of  sulphuretted  hydrogen. 

1963    What  is  nitric  acid  f 

Nitric  acid,  or  aqua-fortis,  is  a  compound  of  five 
parts  of  oxygen  and  one  of  nitrogen. 

It  is  a  liquid ;  when  pure,  colorless,  and  highly  corrosive  ;  it  attacks  al- 
most all  dead,  unorganized  substances,  and  destroys  living  tissues. 

1963  What  is  muriatic,  or,  more  properly,  hydrochloric  acid? 

A  compound  of  hydrogen  and  chlorine  usually  pre- 
pared from  salt.  It  is  an  acid  much  used  in  the  arts. 

1964  What  is  "  lunar  caustic  ?" 

A  compound  of  nitric  acid  and  oxide  of  silver. 

1965  Why,  when  lunar  caustic  is  applied  to  the  flesh,  does  it  burn  and 
destroy  it  ? 


SCIENCE   OF   COMMON   THINGS.  305 


Tanning  of  hides  to  form  leather.  Vinegar  Alcohol.  Yeast. 


Through  the  agency  of  the  nitric  acid  contained  in  it. 

196  6  Do  plants  produce  acids  f 

Acids  are  formed  in  the  vegetable  kingdom  in  great 
abundance  /  they  especially  exist  in  unripe  fruits,  im- 
parting to  them  a  sour  taste. 

Acids  formed  from  mineral  substances  are  called  "mineral  acids;'' 
acids  formed  by  or  from  vegetable  subsiunces  are  called  "  organic  acids." 

196*7   Why  does  tanning  hides  convert  them  into  leather  f 

Hides  are  steeped  in  water,  with  ground  bark  of  the 
oak,  hemlock,  or  other  trees  ;  these  barks  contain  large 
quantities  of  tannic  acid,  which  combines  with  the 
skin  of  animals,  and  forms  a  combination  which  is  in- 
soluble in  water  and  not  subject  to  putrefaction  —  viz. 
leather. 

1968    What  is  ordinary  vinegar  ? 

An  acid,  called  acetic  acid,  and  water. 

I960  If  wine  or  beer  be  imperfectly  corked,  why  does  it  rapidly  turn 
sour? 

Because  air  gets  into  the  liquor,  and  the  oxygen  of 
the  air  combining  with  the  alcohol  of  the  liquor  pro- 
duces acetic  acid,  or  vinegar. 

1970  What  is  alcohol? 

Alcohol  is  the  spirit  existing  in  wine,  beer,  cider, 
etc.,  obtained  in  the  process  of  fermentation. 

1971  What  is  a  ferment  ? 

A  ferment  is  a  substance  containing  nitrogen  in  a 
state  of  decomposition,  which  is  able  to  excite  fermen- 
tation in  solutions  of  sugar  ;  old  cheese,  putrefying 
flesh,  blood,  etc.,  all  of  them  are  ferments. 

1973    What  is  yeast? 

We  apply  the  term  yeast  to  a  particular  species  of, 
ferment  ;  the  foam  of  beer  (or  of  some  similar  liquor), 
produced  by  fermentation. 

1973  Can  you  explain  why  it  is  that  a  body  in  a  state  of  fermentation 
or  putrefaction  should  cause  unlimited  quantities  of  similar  matter  to  pass 
into  the  same  state  ? 


e  only  know  the  f  act  :  the  reason  we  are  ignorant 
of.     The  most  minute  portion  of  milk,  paste,  juice  of 


306  SCIENCE    OF   COMMON   THINGS. 


Fruit,  how  preserved.  Decay  in  wood. 


grapes,  flesh,  or  blood,  in  a  state  of  fermentation  or 
putrefaction,  causes  fresh  milk,  paste,  grape  juice,  flesh, 
or  blood,  to  pass  into  the  same  condition,  when  in  con- 
tact with  them. 

197*4:  In  storing  or  packing  fruit  for  future  use  why  is  it  necessary  tc 
Carefully  remove  every  decayed  specimen  ? 

Because  the  decayed  portions  of  one  specimen  will 
quickly  communicate  decay  to  the  fresh  fruit  in  contact 
with  it,  and  soon  the  whole  mass  of  fruit  will  become 
putrescent. 

197*5  If  in  a  vesssl,  or  any  other  structure,  one  Umber  becomes  decayed 
what  course  ought  to  be  adopted  ? 

It  should  be  removed  immediately,  or  the  decompo- 
sition once  commenced  will  in  time  affect  the  whole 
structure. 

It  sometimes  happens  that  physicians,  in  dissection,  are  seriously  poi- 
soned by  the  slightest  cut  of  a  knife  which  has  been  used  upon  the  dead 
body.  The  knife  introduces  to  the  healthy  blood,  through  the  wound, 
a  minute  portion  of  matter  in  the  state  of  decomposition  or  putrefaction. 
This  acts  as  a  ferment,  and  causes  the  healthy  matter  in  contact  with  it 
to  pass  into  the  same  decomposed  state.  The  action  once  commenced 
rapidly  extends,  until  the  whole  body  becomes  affected,  and  death  ensues. 
It  is  almost  impossible  to  heal  wounds  of  this  character. 

197*0  Why  is  it  especially  dangerous  to  eat  fruit  or  meats  partially 
decayed  f 

Because  the  decayed  portions  of  the  substance  eaten 
are  liable  to  induce  the  same  condition  in  the  healthy 
organs  of  the  stomach  with  which  they  may  come  in 
con  tact. 

1£,  7*7*    Why  do  fruit  preserves  frequently  turn  sour  f 

Because,  owing  to  the  action  of  some  fermenting 
substance  present  either  in  the  fruits  themselves  or  in 
the  air,  the  sugar  used  in  preserving  is  converted  into 
alcohol,,  and  the  alcohol  into  vinegar. 

197*8  Why  does  the  housewife  scald  her  preserved  fruits  to  prevent  their 
turning  sour  ? 

Because  fermenting  substances  and  fermenting  ac- 
tion are  destroyed  by  a  boiling  temperature. 

197*9  Why  do  we  keep  preserves,  beer,  cider,  or  other  substances  liable 
to  turn  sour,  in  a  cool  place  ? 

Because  a  depression  of  temperature  arrests  fermen* 


SCIENCE   OF   COMMON   THINGS.  30? 


"What  is  ether  ?  Disinfecting  agents. 


tation,  though  it  does  not  prevent  its  renewal  when  the 
temperature  is  increased. 

193O    Wliat  is  ether  t 

Ether  is  a  product  obtained  by  distilling  strong  alco- 
hol and  sulphuric  acid.  The  product  is  called  sul- 
phuric ether,  but  it  does  not  contain  sulphuric  acid, 
nor  has  it  any  sulphur  in  its  composition. 

j    1981    What  are  the  properties  of  ether  ? 

It  is  an  exceedingly  volatile,  inflammable  body,  pro- 
ducing insensibility  when  inhaled,  and  readily  dis- 
solving all  fatty  and  oily  bodies. 

1932  Why  will  etlier  remove  spots  of  oil,  paint,  or  grease  from  gar* 
ments? 

Because  it  is  a  solvent  for  all  greasy,  oily  matters. 

1933  What  are  the  best  agents  for  depriving  putrid  and  decaying 
animal  and  vegetable  substances  of  their  offensive  odo^s  ? 

Chloride  of  lime  is  the  most  effectual  agent ;  and 
chloride  of  zinc  and  sulphate  of  iron  (green  vitriol)  are 
also  exceedingly  efficient.  On  a  large  scale,  as  in  the 
sanatory  cleansing  of  towns,  pulverized  charcoal,  burnt 
clay,  and  quicklime,  are  to  be  recommended. 

1984  What  effect  does  the  use  of  perfumes  or  the  burning  of  pastiles 
have  upon  offensive  odors  ? 

They  merely  disguise  the  odor,  but  do  not  remove  or 
destroy  it. 

1935  By  adopting  what  precautions  may  a  person  safely  enter  sick 
rooms,  or  visit,  without  risk,  the  most  dangerous  receptacles  of  filth  ? 

By  moistening  a  linen  cloth  with  vinegar,  and  sprink- 
ling over  it  finely-powdered  chloride  of  lirne. 

Air  breathed  through  this,  applied  to  the  mouth  and  nostrils,  will  enter 
the  lungs  charged  with  a  minute  quantity  of  chlorine,  which  will  effec- 
tually destroy  any  noxious  vapors  or  miasms  that  escape  from  diseased 
bodies,  or  from  decaying  animal  and  vegetable  substances. 

1980  What  three  conditions  are  requisite  to  produce  putrefaction  in 
animal  and  vegetable  substances  ? 

It  is  necessary  that  they  should  be  exposed  to  the 
combined  influence  of  air,  heat,  and  moisture. 

1987  Why  is  a  substance  preserved  from  decay  by  drying,  or  by  tin 
exclusion  of  air  from  it? 


308  SCIENCE    OF   COMMON    THINGS. 

How  smoking  preserves  meat.  What  is  albumen  ? 

Because  by  so  doing  we  remove  the  moisture  and  air 
essential  to  the  process  of  decay. 

19SS  Why  does  the  smoking  of  fish  or  flesh  contribute  to  their  pre- 
servation f 

Because  the  volatile  matters  of  the  smoke,  such  as 
creosote,  pyroligneous  acid,  and  the  like,  effect  a 
species  of  chemical  combination  with  the  fibre  of  the 
meat,  and  with  the  substances  contained  in  the  natural 
juices  of  the  flesh,  which  combinations  are  less  liable 
to  decay  than  the  substances  themselves. 

1989  What  is  albumen  f 

Albumen  is  an  animal  substance  as  well  as  vegetable. 
It  exists  most  abundantly,  and  in  its  purest  natural 
state,  in  the  white  of  an  egg,  from  whence  it  derives  its 
name  (album  ovi\  which  is  the  Latin  for  the  white  of 
an  egg. 

The  serum  or  fluid  portion  of  the  blood  (which,  after  exposure  to  the 
air,  is  separated  from  tlie  more  solid  part)  the  vitreous  and  crystalline 
humors  of  the  eye,  the  brain,  the  spinal  marrow,  and  nerves,  all  contain 
albumen. 

1990  What  is  the  yolk  of  an  egg  f 

This  also  consists  of  albumen,  but  contains  in  addition 
a  yellow  oil,  which  imparts  to  it  its  color. 

1991  Why  is  meat  tough  which  has  been  boiled  too  long  f 

Because  the  albumen  becomes  hard,  like  the  white 
of  a  hard-boiled  egg. 

The  best  way  of  boiling  meat  to  make  it  tender  is  this:  Put  your  joint 
In  very  brisk  boiling  water;  after  a  few  minutes  add  a  little  cold  water. 
The  boiling  water  will  fix  the  albumen,  which  will  prevent  the  water- 
from  soaking  into  the  .meat,  keep  all  its  juices  in,. and  prevent  the 
muscular  fibre  from  contracting.  The  addition  of  cold  water  will  secure 
the  cooking  of  the  inside  of  the  meat,  as  well  as  of  the  surface. 

1993  Why  is  meat  always  tough  if  it  be  put  into  the  boiler  before  the 
water  boils  f 

Because  the  water  is  not  hot  enough  to  coagulate  the 
albumen  between  the  muscular  fibres  of  the  meat, 
which  therefore  runs  into  the  water,  and  rises  to  the 
surface  as  scum. 

1993    Why  -is  Ute  flash  of  old  animals  tough  ? 


SCIENCE  OF   COMMON  THINGS,  309 

What  is  a  poison  ?  Arsenic.  Certainty  of  its  detection. 

Because  it  contains  very  little  albumen,  and  much, 
muscular  fibre, 

1994  What  is  a  poison  f 

A  poison  is  any  agent  capable  of  producing  a  dan- 
gerous effect  upon  anything  endowed  with  life. 

1995  In  cases  of  poisoning  by  substances  taken  into  the  stomach,  what 
course  should  be  pursued,  in  the  absence  ofmedioal  •attendance? 

The  first  step  is  to  evacuate  the  stomach  by  means 
of  powerful  emetics,  and  when  vomiting  has  taken 
place,  warm  water  and  the  white  of  eggs  may  almost 
always  be  given  with  advantage. 

1996  Can  poisons  administered  for  criminal    purposes  be  almost 
certainly  detected? 

They  can ;  chemical  science  within  the  last  few 
years  has  made  such  advances,  that  the  most  minute 
quantities  of  all  the  best  known  poisons  can  be  detected 
with  certainty  long  after  death. 

There  is  no  poison  so  liable  and  certain  to  be  found  as  arsenic,  and  in 
almost  every  case  of  poisoning  with  mineral  poisons,  science  is  enabled  to 
detect  the  substance,  even  when  life  has  been  extinct  for  years,  and  the 
body  nearly  decomposed. 

1997  What  is  arsenic? 

Metallic  arsenic  is  an  exceedingly  brittle  metal,  of  a 
steel-grey  color.  It  vaporizes,  when  heated,  with  a 
strong  odor  of  garlic,  a  property  not  possessed  by  any 
other  metal. 

The  substance  used  as  poison,  and  sometimes  known  as  ratsbane,  is 
arsenious  acid,  a  compound  of  arsenic  and  oxygen.  Arsenious  acid  has 
the  form  and  appearance  of  a  fine  white  powder. 

1998  What  is  the  best  remedy  in  cases  of  poisoning  with  arsenic  f 

The  hydrated  peroxide  of  iron  (iron  rust)*  is  con- 
gidered  the  best  remedy. 

1999  Is  lead  a  poison  ? 

*  The  following  is  the  best  method  for  preparing  this  substance: 
Take  common  copperas  (sulphate  of  iron)  four  ounces ;  dissolve  in  warm 
water  in  a  glass,  or  porcelain  dish,  and  add  a  small  quantity  of  sulphuric 
&cid,  and  afterwards  ammonia  solution,  so  long  as  a  dense  red  precipitate 
is  formed.  This  precipitate  carefully  strained  off,  and  thoroughly  washed 
jn  a  filter  with  water,  is  hydrated  peroxide  of  iron.  So  long  as  kept 
jnoist,  it  may  be  preserved  for  a  great  length  of  time. 


310  SCIENCE   OF   COMMON   THINGS, 

Lead  pipes,  how  poison  -water.  Verdigris.  Calomel. 

Lead  and  nearly  all  its-  compounds  are  dangerous  and 
secret  poisons  ;  when  received  into  the  system,  it  fre- 
quently remains  dormant  for  years,  and  then  suddenly 
manifests  itself  in  various-  forms-  of  disease. 

5000  What  is  the  disease  called  "painters'  colic  f ' 

A  disease  to  which-  painters  and  others  working  in 
lead  are  liable,  in  consequence  of  receiving-  into  their 
system,  imperceptibly,  portions  of  lead. 

5001  Is  it  dangerous  to  sleep  in,  or  Ireathe  the  air  of,  a  room  newly 
painted  with  paints  containing  lead  ? 

It  is  highly  dangerous,  since  the  air  is  filled  with  a 
vapor  of  the  lead  compound  used  as  paint. 

5003  Why  are  some  water s^   when  conveyed  through    lead  pipe, 
poisonous  ? 

"Waters  which  are  very  pure  and  contain  much  oxygen 
dissolved  in  them  ;  waters  which  contain  nitric  acid 
compounds,  such  as  those  flowing  from  the  vicinity  of 
barn-yards,  manure  heaps,  and  those  which  contain 
common  salt  or  organic  matter,  as  water  flowing  from 
swamps  and  fields ;  waters  containing  soluble  car- 
Donates — all  dissolve  lead  from  the  pipes  through 
which  they  may  be  made  to  pass  Constant  use  of 
such  waters,  in  the  process  of  time,  will  introduce  suffi- 
cient lead  into  the  system  to  produce  disease,  which  is 
often  attributed  to  other  causes, 

J2OO3   What  is  verdigris  ? 

Verdigris  is  a  compound  of  copper,  oxygen,  and 
acetic  acid.  This,  and  all  the  compounds  of  copper,  are 
very  poisonous.  The  most  efficacious  antidotes  for 
poisoning  with  copper  are,  white  of  eggs  and  milk. 

5004  What  is  calomel  ? 

It  is  a  compound  of  two  parts  of  mercury  united  to 
one  of  chlorine,  forming  the  sub-chloride  of  mercury. 
The  preparation  commonly  known  in  medicine  as  "  blue 
pill,"  is  a  preparation  of  mercury. 

2OO5    What  is  corrosive  sublimate  f 

A  compound  of  mercury  and  chlorine  united  in  equal 
proportions,  forming  the  perchloride  of  mercury. 


SCIENCE   OF   COMMON   THINGS.  311 

Preservation  of  wood.  Miasm.  Contagion. 

SOO6  Are  loth   these  compounds,  calomel  and  corrosive  sublimate. 

poisons  f 

They  are  /  corrosive  sublimate,  especially,  is  a  most 
deadly  poison.  In  case  of  poisoning  by  it,  the  most 
effectual  antidote  is  white  of  eggs. 

SOOT*  What  is  the  process  of  preserving  wood  from  decay,  commonly 
termed  "  kyanizing  ?  " 

It  consists  in  saturating  the  fibres  of  the  wood  with 
a  solution  of  corrosive  sublimate. 

Poisonous  substances,  and  corrosive  sublimate  especially,  have  the  pro» 
perty  of  protecting  animal  and  vegetable  substances  from  decay.  The 
skins  of  stuffed  birds  and  animals,  and  the  plants  of  a  herbarium,  may  be 
protected  from  insects  and  decay,  by  washing  them  with  a  solution  of  cor- 
rosive sublimate.  It  should  not,  however,  be  forgotten,  that  these  sub- 
stances by  such  treatment  become  themselves  poisonous. 

SOOS    What  is  contagion  ? 

We  apply  the  term  contagion  to  that  subtle  matter 
which  proceeds  from  a  diseased  person  or  body,  and 
which  communicates  the  disease  to  another  person  or 
body. 

Contagion  differs  from  miasm  in  being  the  product  of  disease,  arid  in 
reproducing  itself. 

J2OO9   What  is  miasm  or  miasmata  ? 

Miasm  or  miasmata  is  the  product  of  the  decay  or 
putrefaction  of  animal  or  vegetable  substances,  and 
causes  disease  without  being  itself  reproduced. 

Contagion  occasions  disease  in  the  same  way  that  yeast  excites  fermen- 
tation. Miasm  often  acts,  by  its  chemical  properties  merely,  as  a  poison. 

SO1O  Why  are  contagious  diseases  sometimes  communicated  to  indi- 
viduals who  merely  approach  the  vicinity  of  diseased  persons,  but  do  not  come 
in  contact  with  or  even  see  them  ? 

Because  the  air  itself,  which  has  been  in  contact  with 
the  diseased  persons,  carries  with  it  the  seeds  or  germs 
of  infection,  and  thus  communicates  disease,  sometimes 
at  great  distances. 

SOU  Why  are  not  all  persons  affected  alike  when  exposed  to  similar 
contagious  diseases  ? 

Contagious  matter  is  not  capable  of  producing  dis- 
ease, unless  a  compound  is  present  in  the  system  capable 
of  being  decomposed  ly  contact  with  the  exciting  body. 


312  SCIENCE   OF   COMMON   THINGS. 

Susceptibility  to  contagion.  Nutritive  value  of  food. 


SO1S    What  do  we  mean  by  susceptibility  to  contagion  f 

We  mean  that  the  blood  of  a  person  contains  sub* 
stances  by  the  decomposition  of  which  the  exciting  body 
or  contagion  can  be  reproduced.  If  these  substances 
are  not  present,  and  if  the  system  be  perfectly  healthy, 
contagion  will  i'ail  to  produce  disease. 

J3O13  What  is  the  relative  nutritive  value  of  the  different  kinds  of  meat 
Us  food  f 

The  relative  nutritive  value  of  the  different  meats  for 
food  is  as  follows :  beef  is  the  most  nutritious  /  then 
chicken,  pork,  mutton,  and  veal. 

2014  What  varieties  offish  are  the  most  nutritious  f 

The  haddock,  the  herring*  the  salmon,  and  the  eel,  in 
order. 

2015  What  vegetable  of  ordinary  consumption  is  tht  most  nutritious  f 

The  cabbage. 


INDEX. 


ABSORPTION  of  light,  261 

of  heat,  172 

Abutment,  what  is  an,  45 
Acetic  acid,  305 
Acids  of  plants,  305 
Acid,  what  is  an,  303 
Action  and  reaction,  explained,  28 

illustrations  of,  28 
Adhesion,  what  is,  12 
Adult,  oxgyen  respired  by  an,  per  hour, 

209 

Aerolites,  general  appearance  of,  95 

definition  of,  94 

velocity  of,  95 

weight  of,  95. 

Affinity,  what  is,  193 

Air,  always  contains  moisture,  91 

in  motion,  212 

breathed  twice  unwholesome,  205 
condensed  by  cold,  75 
currents  of.  in  an  occupied  room,  212 
exists  in  all  water,  55 
expanded  by  heat,  75 

proof  of,  75 
fresh,  how  much  required  per  hour 

for  breathing,  210 
heated,  ascends,  204 

how  proved,  205 
how  ascends  in  chimneys,  215 
how  escapes  from  the  lungs,  72 
how  heated  and  cooled,  74,  75 
impenetrable,  68 
in  motion,  why  feels  cool,  153 

spring,  why  chilly,  138 
necessary  for  the  production  of  sound, 

porous.  63 

atmospheric  composition  of,  63 

weight  of,  00 

how  proved,  69 
when  rarefied,  70 
A/Jbumen,  in  eggs,  308 


Albumen,  in  meat,  308 
what  is,  308 
Alcohol,  what  is,  305 
tVlkali,  what  is,  303 
Angle,  definition  of,  251 
Animals,  change  of  color  in  winter  of,  274. 
ector  of  arctic,  175 
distribution  of,  142 
foretell  changes  in  the  weather, 

113 

the  strongest,  33 
Apples,  unripe,  why  sour,  303 

when  sour  and  when  sweet,  303 
Aqueducts,  principle  of  construction  of,  50 
Aqua-fortis,  what  is,  304 
Architecture,  defined,  41 

origin  of  the  varieties  of,  41 
Architrave,  47 
Arsenic,  poisoning  by,  309 

what  is,  309" 
Arch,  what  is,  43 

when  invented,  43 
Ashes,  how  preserve  a  fire,  228 
Atmosphere,  amount  of  carbonic  acid  gas 

in,  207 
height  of,  70 
not  invisible,  69 
pressure  of,  71 
what  is  the,  69 
Atom,  what  is,  5 
Attraction,  what  is  an,  11 
Aurora  borcalis,  cause  of,  287 
height  of,  288 
occurs  by  day  aa  well  as 

by  nisrht,  2S9 
utility  of,  2S9 
what  is,  2S7 
where  seen,  287 
Avoirdupois  weight,  origin  of,  20 


Ball,  elastic,  why  rebounds,  23 


INDEX. 


Balusters,  what  are,  45 
Balloon,  why  rises  in  the  air,  13 
Bark,  how  especially  adapted  as  a  cover- 
ing for  trees,  157 
Barometer,  construction  of,  102, 103 

heat  and  cold  no  effect  on,  113 
how  differs  from  a  thermo- 
meter, 104 

how  invented,  101, 102 
tube,  why  left  open,  104 


iBuilding,  properties  of  a  good,  41 
Buildings,  principle  of  warming  and  von- 

t;  latins,  204 

Burning'point,  what  is,  222 
Burns  on  the  skin  affect  respiration,  235 


Calomel,  what  Is,  310 


use  of,  for  determining    the  Caloric,  meaning  of  term,  181 


state  of  the  weather, 
Base  of  a  column,  46 
Battery,  galvanic,  291 

/oles  of,  292 
in  "~ 


Beams,  strength 


different  positions. 


Bed  coverings,  the  warmest,  213 


india-rubber,  why  not  used  Capital  of  a  column,  46 


for,  218 

feather,  safe  place  in  a  thunder  storm, 
2S3 


Candle,  why  burns  when  lighted,  281 
Cannon,  distances  to  which  they  can  send 

a  ball,  35 

varieties  of,  35 

Capillary  attraction  defined,  65 

vessels,  action  of,  237 

what  are  they,  236 


Carbon,  more  thrown  off  from  the  system 

in  winter  than  in  summer,  240 
what  is,  224 


Carbonic  acid,  sources  of,  212 
gas,  206 

a  poison,  207 


Beer,  why  turns  sour,  805 

Bell,  cracked,  why  discordant,  119 

metal,  composition  of,  116 

sound  of,  stopped  by  touching  it,  118  where" found,  206 

Bellows,  use  of  in  kindling  a  fire,  229         |Cat,  fur  of,  why  sparkles  in  cold  weather, 
Birds,  how  enabled  to  fly,  26  278 

why  stretch  out  their  necks  in  fly-  Cats,  why  see  in  the  dark,  267 


ing,  27 
Black,  the  absence  of  color,  not  a  color, 

270 

why  some  bodies  are,  270 
Blankets,  why  warm,  14S 
Blood,  arterial  and  venous,  237 

color  of,  237 

how  affected  by  oxygen,  205 
Blowers,  of  grates,  &c.,  use  of,  217 
Boats,  life,  how  prevented  from  sinking, 

Body,  a,  how  far  it  can  fall  in  one  second, 


Cellars,  why  cool  in  the  summer,  151 
warm  in  the  winter,  151 
Cement,  definition  of,  38 
Cements,  hydraulic,  39 
Centrifugal  force,  23 

illustrations  of,  23,  24 
Chalybeate  waters,  54 
Champagne,  why  sparkles,  73 
Charcoal,  how  made,  224,  225 

what  is,  224 

why  black,  261 
Chemistry,  familiar,  302 


28  Children,  why  difficult  to  learn  to  walk, 

what  is  a,  4  18 

Boiling  point,  influence  of  atmospheric  Chimney,  fire  in,  how  extinguished,  230 

Chimneys,  how  quicken  the  ascent  of  hot 

air,  215 
of  manufactories,  why  usually 

very  long,  215 
principles  of  construction  of, 


pressure  on,  157, 1S8 
of  a 


liquid,  155 
Bones,  hollow  cylinders,  37 
Boots,  why  cannot  a  man  raise  himself  by 
pulling  on  the  straps  of,  23 


Bottle,  why  gurgles,  73 
Bottles  of  ale  and  cider,  why  frequently 
burst,  74 


216 

smoke  under  what  circumstan- 
ces, 216 


Bouquets,  arrangement  of  flowers  in,  273    Choke-damp,  what  is,  211 

Breakers,  what  are,  61  j Church,  crowded,  persons  in  feel  drowsy, 

Breath,  why  visible  in  winter,  and  not  in'     210 

summer,  89  Circuit,  galvanic,  292 

Breathing  on  glass,  why  dulls  it,  88  ! Cities,  air  >f,  less  pure  than  the  country, 

why   difficult  at   a  very  high     210 

elevation,  72  Cleanliness,  necessity  of,  233 

Bricks,  burned,  why  red,  39  jClimate,  meaning  of  the  term,  104 

why  used  for  lining  stoves  and  fur-  Climates,  peculiarities  of,  104 

naces,  151  temperature  of,  coloration  pecu- 

Broth,  cooled  by  convection,  159  liar  to,  271 

Bubbles,  air,  in  ice,  origin  of,  178  '•  Clock,  common,  what  is  a,  29 

in  a  tea-cup,  how  attracted,  14      Clocks,  why  go  faster  in  winter  than  ia 
on  leaves  of  water  plants,  what     the  summer,  30 

are  they,  236  Clothing,  contains  no  warmth  in  itself; 

eoap,  why  ascend,  56  |     152 


INDEX*. 


315 


regetabl*  De 


Clothing,  how  makes  us  warm,  147 

use  of,  148 

Clouds  and  fog,  difference  between,  80 
Clouds,  cause  of  their  various  shapes 

appearances,  86 
color  of,  85 

distance,  above  the  earth,  84 
size  of,  84 

sunset,  why  colored,  86 
what  are,  83 
when  high  and  low,  83 
ffoai,  anthracite,  225 
bituminous,  225 
deposits,  extent  of,  227 
mineral,  origin  of,  225 

produced    from    v 

matter,  225 
Cohesive  attraction,  11 

illustrations  of,  12 
Cold,  greatest  artificial,  134 
natural,  134 

how  occasioned  by  wet  clothes,  197 
what  is,  130 
Color,  does  not  exist  in  the  dark,  270 

influence  of,  on  the  deposition  of 

dew,  168 

Colors,  artificial,  why  fade  in  the  sun,  271 
dark,  optical  effects  of,  upon  the 

size  of  the  figure,  273 
iSght,  effect  of,  274 
disadvantages  of  a  dress  of  uniform, 

most  conspicuous  in  battle,  274 
peculiar  to  arctic  regions,  272 
seven  primary,  255 
warmest  for  dresses,  175 
Columns,  why  larger  at  the  bottom  than 

at  the  top,  42 

Combustion,  a  process  of  oxidation,  220 
chemical  action  of,  221 
essential  requisites  of,  221 
spontaneous,  illustrations  of. 

230 

what  is,  220 
Compass,  does  not  always  point  north  and 

south,  297 
mariner's,  279 

how  constructed,  297 
when  discovered,  297 
Compasses,  ships',  how  affected  by  light- 
ning, 299 

Compressibility,  6 
Concord  «i«l  -discord,  what  arc,  120 
Contagion,  susceptibility  to,  810 

what  is,  811 

Convection  of  h-eat,  153 
Copper,  poisonous  effects  of,  310 
Cornea,  effect  of  flattening,  265 

of  the  eye,  263 
Cornic<s,  what  is  a,  47,  48 
Corrosive-sublimate,  what  ts>  810 
Coughing,  what  is,  122 
Countries,  least  cloudy,  10S 
most  cloudy,  107 
some,  why  destitute  of  rain, 

110 

Cowl,  use  of,  upon  a  chimney,  216 
Cream-,  why  rises  upon  milk,  64 


Crying,  what  Is,  123 

Cultivation,  how  increases  the  "warmth  of 

a  country,  198 
and  Curtain,  behind  a  pulpit,  influence  of  on 

sound,  126 
Cylinder,  strength  of -a,  36 


Dead  body,  whycold,238 

Decay  ift  substances,  how  occasioned  and 

promoted,  806 
Density,  what  is,  6 
Diseases,  when  contagious,  811 
Dew  and  rain,  difference  between,  163 
Dew,  cause  of,  164 

deposited    most   readily   on    cleat 

nights,  163 
does  not  fall,  168 
does  not  form  on  exposed  parts  (# 

the  human  body,  reason  of,  170 
falls  abundantly  on  cultivated  soils, 

none  on  a  windy  night,  164 
none  on  cloudy  nights,  163 
phenomenon  of,  162 
rarely  observed  in  cities,  168 
when  converted  into  frost,  163 
when  most  copious,  166 
why  more  abundant  0*1  some  sub- 
stances than  others,  164 
why  rolls  in  drops  on  fcavcs,  169 
Dewdrop,  why  round,  168     . 
Diamond,  cause  of  its  brilliancy,  256 
Disinfecting  agents,  307 
Distillation,  how  effected,  196 

what  is,  195 
Divisibility  of  matter,  5 
Doors,  why  shrink  in  dry  weather,  199 
swell  in  damp  weather,  199 
Dovetailing,  what  is,  44 
Draining  lands,  promotes  warmth,  198 
Draught  of  air,  occasion  of,  214 
a  chimney,  214 

stove,  214 

v/hcn  there  is  none,  215 
Dress,  arrangement  of  colors  in,  272,  273 
Presses,  white^"  why  adapted  for  summer, 


Drum,  why  sounds,  121 

Drying  and  distilling,  difference  between^ 

1$6 
Ducks,  why  not  made  wet  with  water, 

169 

Ductility,  11 
Dust,  how  expelled  from  a  crtat  or  carpet 

by  beating,  26 
Dunghill,  cause  of  the  heat  t>f,  229 


Car,  construction  of,  115 

drum  of,  114 
Sarthen  vessels,  why  crack  in  cold  we* 

thcr,  180 
Earth,  heat  of,  136 


315 


IHDEX, 


Earth,  how  proved  to  be  in  motion,  22 
poles  of,  296 
temperature  of,  influence  on  the 

distribution  of  animals,  142 
why  made  colder  after  sunset,  162 
Earthquakes,  probable  cause  of,  136 
Ebullition,  what  is,  155 
Ech6,  distance  necessary  to  produce,  125 
what  is,  124 

why  sometimes  double,  125 
how  produced,  124 
where  heard  in  greatest  perfection, 

124 

Edge,  straight,  243 
Eel,  electrical,  279 
Elastic  bodies,  what  are,  8 
Electricity,  275 

and  lightning,  identity  of,  285 

how  proved,  285 1  Figure,  5 
connection  of  light  and  heat,  |  Filtration,  principles  of,  7 


Exercise  \vhy  makes  us  xvarm,  238 
Expansion  by  heat,  176 


Falling  bodies,  laws  of,  25 

Fan,  a,  does  not  cool  the  air,  174 

Fanning  the  face,  why  cools,  173 

utility  of,  174 
Far-sightedness,  cause  of,  265 

how  remedied,  265 

Fat  people,  why  throw  back  their  shoul- 
ders, 17 

Feathers,  why  called  light,  6 
Feather,  how  attracts  the  earth,  14 
Ferment,  what  is  a,  305 
Fermentation,  how  induced  by  yeast,  305 


278 

conductors  of,  276 
galvanic,    greatest   quantity, 

how  excited,  292 
galvanic  of  two  kinds,  posi- 
tive and  negative,  291 
how  called  into  action,  275 
how  excited  by  rubbing  the 

fur  of  a  cat,  278 
invisible,  275 

natural  agents  active  in  pro- 
ducing, "279 
non-conductors  of,  277" 
of  muscular  action,  279 
positive  and  negative,  278 
produces  heat,  136 
velocity  of,  278 

Electric  cloud,  discharge  of,  2SO 
Electrical  machines,  how  constructed,  277 

repulsion,  276 

Electrified  and  non-electrified  bodies,  276 
Electro-magnetism,  what  is,  299 

when   and    how  disj 

covered,  299 
metallurgy,  294 

principles  of,  294 
Electrotype  process,  294 
Entablature,  47 

Equinoxial  storm,  does  it  occur,  112 
Esquimaux,  why  fond  of  oil  and  fat,  230 
Ether,  how  removes  grease,  307 

what  is,  307 
Evaporation,  daily  amount  from  the  sea, 

110 

effects  of,  197 
phenomena  of,  195 
Eye,  human,  structure  of,  262 
muscles  of,  262 
parts  of,  263 
retina  of,  263 

pained  by  sudden  light, .266 
pressure  on,  occasions  the  sensation 

of  light,  26S 

Eyes,  do  not  see  alike  with  both,  263 
Eyebrows,  use  of,  266 
Eyelashes,  use  of,  266 
Exertion,  disagreeable    in  hot   weather, 
why,  240 


Fire,  benefit  of  stirring  a  dull,  230 
caused  by  friction,  139 
heat  of,  cause  of,  229 
intensity  depends  on  what,  230 
reflection  of,  in  our  windows,  250 
what  is,  222 

why  feels  hot  as  we  approach  it,  161 
whv  placed  near  the  floor  of  a  room, 

160 
in  the  niirht,  why  difficult  to  judge  of 

the  distance  of,  269 
places,  open,  advantages  of,  219 

not  economical,  218 
Flame,  candle,  hottest  part  of,  232 
color  of,  231 

luminosity,  depends  on  what,  222 
of  a  lamp  or  candle,  analysis  of, 

232 
of  a  candle,  why  points  upwards, 

232 

solid  particles  in,  222 
what  is,  222 

when  will  it  smoke,  223 
Flames,  why  all  not  equally  luminous,  231 
Flues  of  stoves,  why  covered  with  black- 
lead,  162 
Flannel,  how  preserves  ice  from  melting, 

143 
Fluids,  laws  and  phenomena  of,  49 

two  classes  of,  49 
Flying,  how  differs  from  leaping,  28 
Force^  what  is,  22 
Food,  hot,  cooled  by  blowing,  159 

the  fuel  of  the  body,  238 
Fogs,  cause  of,  84 

when  and  where  occur,  90 
why  does  not  become  dew,  S9 
Franklin's,  Dr.,  theory  of  electricity,  277 
Friction,  what  is,  22 

action  of  in  exciting  electricity, 

275 

Frieze,  in  architecture,  47 
Frost,  hoar,  what  is,  187   ^.^ 

rare  under  trees  and  shrul 

1S5 
how  a  thin  covering  protects  plants 

from,  167  • 
readers  the  earth  friable,  184 


INDEX. 


317 


Frost-work  on  windows,  cause  of,  185 
Fruit,  precautions  to  be  used  in  packing, 

306 
Fuel,  elements  of,  228 

perfect  combustion  of,  bow  attained, 

220 

Furnaces,  hot  air,  how  constructed,  219 
Furs,  why  used  for  clothing,  147 
Fumigation,  301 


Galvanism,  how  discovered,  289 

produced,  290 

simple  experiment  illustrat- 
ing, 290 
what  is,  289 

Galvanl,  discovers  galvanic  electricity,  290 
Galvanic  battery,  ordinary  effects  of,  293 
Gas,  what  is  a,  8 
Gases,  law  of  diffusion  of,  207 

not  all  invisible,  68 
Glacier,  what  is  a,  106 
Glaciers,  where  occur,  106 
Glass,  burning,  a  double  convex  lens,  260 

ground  for  shades,  use  of,  233 
Glasses,  burning,  131 
Gold,  melting  point  of,  135 
Gothic  architecture,  origin  of,  45 
Grain-weight,  origin  and  construction  of, 

20 

Grapes,  ripe,  why  sweet,  303 
Grass,  grown  in  the  dark,  of  a  light  color, 

272 

Gravitation,  what  is,  13 
Gravity,  centre  of,  15 

illustrations  of  the  laws  and  prin- 
ciples of,  15,  16 

Oreasing  carriage  wheels,  use  of,  140 
Greasy  food,  why  relished  in  cold  wea- 
ther, 239 
Green  colors  suited  to  fair  complexions, 

2T3 
Grindstones,  In  rapid  motion  why  often 

burst,  23 
Gun,  essential  properties  of,  35 

how  we  take  aim  with  a,  244 
Gunpowder,  composition  of,  34 
power  of.  34 

when  and  how  discovered, 
35 


II 


Habitations,  probable  form  of  the 

human,  41 

Hail,  what  is,  and  how  formed,  94 
Hair,  use  of  in  mortar,  40. 
Halls,  for  speaking,  how  constructed,  126 
Hardness,  what  is~  10 
Headache,  how  produced  by  bad  air,  209 
Hearth-rugs,  why  feel  warm,  145 
stone,  why  feel  cold,  145 
Heat  and  cold,  sensations  of,  131 

animal,  cause  of,  236 

best  conductors  of,  144 


Heat,  effects  on  the  dissolving  power  ol 

liquids,  194 
effects  of,  131 
effects  of,  on  the  bulk  of  some 

liquids,  ITS 
expands  all  bodies,  176 

illustrations  of,  177 
has  no  weight,  130 
how  communicated,  143 

illustrations  of,  4 
how  diffused,  130 
how  evolved  by  combustion,  221 
how  measured,  187 
good  absorbers  of,  not  gooo*  reflect- 
ors, 171 

greatest  artificial,  how  produced,  293 
greatest  artificial,   how   measured, 

134 
illustrations  of  radiation    of,    161, 

162 

In  ice,  130 
latent,  what  is,  138 
occasioned  by  chemical  action,  il- 
lustrations of,  137 
of  the  sun,  132 
produced  by  friction,  140 
radiant,  160 
rays  of,  171 
reflection  of,  171 
solar,  extends  below  the  earth's  sur« 

face  how  far,  136 
sources  of,  132 

sun's  differs  from  artificial,  133 
velocity  of  transmission  in  different 

substances,  illustrations  of,- 144 
vital,  illustrations  of,  141 
what  is,  129 

Health  injured  by  reduction  of  the  tempe- 
rature of  the  body,  198 
Height  from  which  a  body  falls,  how  cal- 
culated, 29 

Hiccough,  what  is,  123 
Hides,  how  converted  into  leather  by  tan- 
ning, 305 

Horizon,  what  is,  269 
Horse-shoe  magnets,  298 
Horse-power,  what  is,  33 
House,  part  most  dangerous  in  a  thunder 

storm,  282 

House,  haunted,  origin  of  stories  concern- 
ing, 128 

Hurricane,  what  is  a,  80,  81 
Hurricanes,  where  prevail,  80 
Huts,  first  form  of  human  habitations, 

41 

Hydrochloric  acid,  304 
first  Hydrogen  gas,  its  properties,  224 

the  lightest  of  all  bodies,  62 
sulphuretted,  304 
how  formed,  304 
what  is,  224 
Hydrostatics,  definition  of,  49 


Ice,  "  anchor,"  what  is,  179 


318 


INDEX. 


Ice,  fractures  in  regular  Hues  and  aagles,  Light,  chief  sources  of,  241 


186 
heat  of,  180 
what  is,  179 

why  floats  upon  water,  62 
why  melted  by  the  sun,  196 
Icebergs,  height  of,  106 

how  formed,  106 
Illusions,  optical,  269 
Images  all  appear  inverted  in  water,  246 
Impenetrability,  4 
Incandescence,  what  is,  181 
Incidence,  line  and  angle  of,  246 
Induction  in  magnetism,  296 
Inertia,  illustrations  of,  10 
Inertia,  what  is,  9 

Insects,  how  occasion  sounds,  123, 124 
Instrument,  stringed,  use  of  the  body  ot, 

117 

Ionic  order  of  architecture,  45 
Iris  of  the  eye,  263. 
Iron,  how  made  hot  by  striking,  139 
meteoric,  96 
where  found,  96 
why  sinks  in  water,  62 
•why  stronger  than  wood,  12 


Kettle,  why  heat  is  not  applied  at  the  top 
of,  154 

why  sometimes  boils  over,  156 
Kyanizing,  what  is,  311 


Lakes,  some  never  frozen,  183 

Lamps,  closed,  use  of  a  hole  in  the  top, 

233 

gas  generated  by,  208 
smokes,  occasion  of,  223 
solar  and  astral,  how  constructed, 

223 
wicks,  eottoa  best  adapted  for, 

Land,  configuration  of,  effect  on  tempe- 
rature, 107 

Latent  heat,  what  is,  189 
Larynx,  122 
Laundress,  why  boils  starch,  802 


how  propagated,  244 

intense,   why  causes  pain  to  th« 

eye,  266 

most  splendid  artificial,  how  pro- 
duced, 293 

moves  in  straight  lines,  244 
of  the  sun,  how  much  intercepted 

by  the  atmosphere,  261 
possesses  no  weight,  241 
ray  of,  when  reflected,  244,  245 
refraction  of,  2-54 

the  same  quantity  not  reflected  at 
all  angles,  illustrations  of  thi» 
principle,  248 

velocity  of,    how  estimated;  illus- 
trations of,  242,  243 
what  is,  241 

white,  composition  of,  255 
why,  when  it  is  cloudy,  252 
zodiacal,  97 
Lightning  clouds,  height  above  the  earth, 

280 
conductors,  best  materials  for, 

284 

different  kinds  of,  280 
direction  of  a  flash  of,  281 
does  not  follow  a  direct  path, 

284 

heat,  cause  of,  281 
how  kills  persons,  281 
rod,  what  is  a,  284 
rods,  how  fastened  to  buildings, 

285 

how  protect  houses,  2S4 
when  productive  of  harnv, 

284 
why  terminate  in  points, 

284 

sheet,  280 
what  is,  280 
why  most  common  in  summer, 

281 

Lights,  Northern,  287,  288 
Lime,  chloride  of,  307 
quick,  38 

absorbs  carhpnic  acid,  212 
slacked,  38 
water  poured   on    occasions   heat, 

how,  137 
Linen  handkerchief,  why  preferred  to  A 

cotton  one,  149 

Linen,  how  dried  by  exposure  to  the  air, 
198 


why  touches 
saliva,  195 
Laughing,  what  is,  123 
Lead,  a  poison,  310 

why  called  heavy,  6 
Leather,  how  made,  805 


Leaves,  of  plants,  how  radiate  heat,  165 
of  plants,  why  green,  271 
why  brown  in  autumn,  271 
Lens,  double  convex,  260 

what  is  a,  260 

Lenses,  different  varieties  of,  260 
Li«ht,  absorption  of,  261 

trtmcialt  vn  what  depends,  231 


flat-iron  with!  why  cooler  thnn  cotton,  149 

Liquefaction,  192 
Liquid,  what  is  a,  8 
Liquids,  how  to  cool,  155 

impart  no  additional  heat  after 
they  boil,  157 


Liquors,  frothing,  cause  of,  74 
Loadstone,  what  is  a,  295 

why  so  called,  295 

Loudness,  of  sound,  on  what  depend?.,  US 
Lunar  caustic,  304 
Lungs,  description  of,  234 


INDEX. 


319 


vantages  of,  31 


Machine  and  a  tool,  difference  between,  Mortar,  why  becomes  hard,  33 


31 
rhat  Is  a,  31 


,31 


Machinery  does  not  create  power, 
Magnet,  directive  power  of,  296 

what  occurs  when  one  is  broken, 

293 
Magnets,  horse-shoe,  293 

how  constructed,  297 
natural,  where  found,  295 
weights,  great,  lifted  by,  ? 
Magnetism,    communicated    by   contact, 

295 
connection  with  electricity, 

295 

Malleability,  11 
Man  alone  capable  of  enduring  all  tempe- 
ratures, 143 
method  in  which  he  can  exert  the 

greatest  strength,  33 
on  a  church  spire,  why  scorns  very 

small,  251 

shrinks  when  starved,  233 
Maps,  coast  survey,  how  produced,  294 
Mastich,  or  mastic,  40 
Matches,  how  ignited  by  friction,  141 
Materials,  strength  of,  36 

illustrations  of,  36 
Matter  defined,  3 

evidence  of  its  existence,  3 

limits  to  the  division  of,  5 

particle  of,  5 

properties  of,  4 

the  strongest  form  in  which  it  can 

be  arranged,  36,  37 
Miasm,  or  miasmata,  311 
Milk  boils  more  readily  than  water,  155 
Mirror,  how  we  see  ourselves  in  a,  245 

why  images  appear  behind  a,  247 


Moon,  why  seems  a  flat  surface,  251 

why  seems  larger  than  tho  stare, 


Mortare,  composition  of,  38 

Mortising,  what  is,  42 

Motion,  22 

Mountains,    distant,    why    appear 


bluo, 


high,  why  covered  with  snow, 

105 

Mountain  tops,  why  cold,  172 
Muriatic  acid,  304 
Muscular  energy,  how  exerted,  33 
Music,  scale  of,  121 
Musical  instruments,  how  occasion  sound, 

sounds,  what  are,  120 


N 

Nails  in  old  houses,  why  loose,  187 
Near-sightedness,  cause  of,  264 

how  remedied,  265 
Needle,  magnetic,  296 
Negro's  skin  never  blisters  from  the  sun, 

174 

Nitric  acid,  304 

Nitrogen,  its  properties  and  uses,  205 
what  is,  205 


Objects,  how  we  judge  of  the  sizo  and 

position  of,  250 
Ocean,  colors  of  animals  in,  272 

depth  to  which  light  penetrates, 

Odors,  307 

Oersted,  Prof.,  his  discovery,  299 


Mirrors,  245  Oil  and  water,  why  not  mix,  193 

Mist  and  fog,  distinction  between,  89          Opaque  bodies,  261 
Meat,  how  preserved  by  smoking,  303        Orders  in  architecture,  45 

when  tough,  303  'Owls,  why  see  in  the  dark,  267 

Medicines,  prescription  by  drops  unsafe,  Oxygen,  now  much  required  per  hour, 


Mercury,  freezes  at  what    temperature, 

191 
of  a  barometer,  why  sinks  in  fine  Oxidation,  what  is,  220 

weather,  104 
when  freezes,  134 
Metals,  why  melted  by  fire,  192 
Meteorites,  how  supposed  to  originate,  96 

what  are,  94 

Meteorology,  what  is,  74 
Mist  and  fog,  why  vanish  at  sunrise,  164 
Mist,  on  windows,  cause  of,  87 


209 

its  properties  and  uses,  205 
what  is,  205 


Paint,  in  tho  vicinity  of  sowers,  why  dis- 
colored, 304 

how  preserves  wood,  152 
Paints,  lead,  when  dangerous,  310 


Mixture  and  solution,  difference  between,  Paper,  blotting,  why  absorbs  ink,  66 


193 
Moon,  lisht  of,  seems  to  make  a  path  in 

'the  water,  249 
influence  of,  on  the  weather,  111 


light,  how  occasions  putrefaction,  Pendulums,  compensating,  187 


112 

why  appears  largo  on  the  borkon, 
269 


writing,  why  will  not  absorb  ink, 

66 

Paste,  adhesiveness  due  to  irhat,  303 
Pedestal,  what  is  a,  46 


length  of,  that  beats  seconds, 

29 
what  fa  a,  29 


320 


INDEX. 


Persons,  why  many.  ROC  the  same  object  Rain,  none  if  the  air  be  dry,  104 


at  the  same  time,  244 
Perpetual  motion  in  nature,  23 
instance  of,  23 
Perspiration,  insensible,  what  is,  S3 

why  caused  by  active  exer- 
tion, 239 

Pilasters,  what  are,  45 
Pile,  what  is  a,  42 

Pipes,  lead,  how  affected  by  water,  310 
water,  why  liable  to  burst  in  freez- 
ing, 1S1 

Pisa,  leaning  tower  of,  17 
Planets,  how  give  light,  242 
Plants,  how  purify  the  water,  236 

respire  as  well  as  animals,  235 
water,  liberate  oxygen,  236 
Platina,  the  heaviest  substance  known, 

62 

Plastic  bodies,  what  are,  9 
Plinth  of  a  column,  46 
Pneumatics,  what  is,  49 
Poison,  what  is  a,  309 
Poisoning,  what  to  do  in  cases  of,  309 
Poles  of  a  galvanic  battery,  292 
Pores  of  a  body,  6 
Portico,  what  is  a,  45 
Potatoes,  frozen,  why  sweet,  303 
Potato,  starch  constitutes  the  bulk  of,  302 
Posver,  how  we  apply  it,  31 
horse,  33 
of  gunpowder,  34 
sources  of,  32 
steam,  34 
water,  33 

Preserves,  why  turn  sour,  306 
Prism,  how  separates  a  ray  of  light,  255 
Pump,  chain,  what  is,  100 
common,  98 

forcing,  construction  of,  100 
height  to  which  water    may   be 

raised  by,  99 
why  water  rises  in,  100 
Pupil  of  the  eye,  263 

contracts   by  a  sudden 

light,  266 

Putrefaction,  causes  of,  307 
Putty,  what  is,  40 
Pyrometers,  how  constructed,  191 


origin  of,  91 

water,  why  called  soft,  56 

where  most  abundant,  103 

why  cooler  after,  199 

why  falls  in  drops,  91 

yearly  amount  falling  in  different 

parts  of  the  earth,  IDS 
Rainbow,  formation  of,  257 

when  seen,  257 
Rainbows  at  waterfalls,  253 

double,  when  seen,  253 

no  two  persons  see  the  same, 

253 

Rain-gauge,  what  is  a,  109 
filed  rays  of  light  possess  the  greatest  beak 
!     ing  effect,  272 
'Reflection,  line  and  nnglc  of,  246 

of  light,  24o 

Reflectors  of  heat,  what  arc  good,  171 
RefraagibiUty,  86 
Refraction  of  light,  254 
Remedies  for  poisons,  309,  310 
Repulsion,  what  is,  11 
Resonance,  what  is,  125 
Respiration  a  form  of  combustion,  234 
object  of,  234 
what  is,  233 
Retina  of  the  eye,  263 
Retort,  what  is  a,  195 
.Rifle,  advantages  of,  over  a  musket,  35 
River,  always  seems  more  shallow  than  it 

is,"255 

bottom,  rarely  frozen,  181 
part  in  which  the  water  runs  most 

rapidly,  50 
Rocks  and  stones  retain  moisture,  107 

cause  of  their  rounded  and  weather- 
worn appearance,  179 
why  often  split  in  cold  weather, 

ISO 

Roman  cement,  39 
Room,  air  of.  how  affected  by  a  current 

209 

coolest  part  of,  117 
hottest  part  of,  217 
Rose,  why  red,  270 
SRust,  what  is,  222 


Salt,  how  dissolves  ice,  1S4 
Qnadrrfpcd,  never  raises  both  feet  on  a,  lakes,  origin  of,  5S 

side  at  once,  17  utility  of,  in  the  ocean,  58 

Quadrupeds,  why  swim  easier  than  man,|Sand,  best  suited  for  mortar,  39 


63 
Quick  lime,  what  is,  33 


Radiators,  good,  of  heat,  161 
Radiation,  160 

of  heat,  on  what  depends,  161 
Rain  drops,  form  of,  169 

why  spheres,  160 
Low  measured,  109 


Savages,  how  hear  by  placing  the  ear  closo 

with  ground,  117 
Scarfing  and  interlocking,  43 
Sea  breeze,  why  cool,  79" 

effect  of,  on  temperature,  107 

rarely  freezes,  Ib3 

water,  why  freezes  less  readily  than 
fresh  water,  135 

why  not  full,  199 

why  salt,  47 

vapor  of,  not  salt,  199 
Seasons,  alternation  of  warm  and  cold,  112 


INDEX. 


321 


Seeing,  sense  of,  how  exerted,  241  iBounds,  when  flat,  121 

Senses,  number  of,  3  why  seem  louder  in  a  church  than 

what  are  th'jy,  3  in  a  plain,  128 

Sewers,  foul,  why  destructive  to  health,  Soup,  why  keeps  hot  longer  than  water, 

Shade,  why  cool  in  the  summer,  150  'Sparks  of  fire,  what  arc,  7 

why  objects  seeui  dark  in,  252          Specific  gravity  defined,  62 
Shadow,  what  is  a,  244  iSpeetacles  best  suited  for  old  people,  265 

Shaft  of  a  column,  46  Spoon,  metal,  how  retards  the  boiling  of  a 

Sheets  of  a  bed  why  feel  cold,  and  the  kettle,  150 

blankets  wann,  152  why  tarnisbod  by  the  yolk  of  eggs, 

Ship  at  sea,  why  the  masts  are  seen  before  304 

the  hull,  253  Spray  of  waves,  cause  of,  61 

Ships,  iron,  why  do  not  sink,  65  Springs,  effect  of  drainage  upon,  53 

Sbces,  hotter  for  being  dusty,  172  Stones  for  building,  bo\v"  to  estimate  their 

Skull,  the  form  of  the,  embodies  the  prin-  durability,  43 

ciples  of  the  arch,  44  building,  action  of  the  weather 

Sight,  difficult  after  leaving  a  lighted  room  on,  48 

and  going  into  the  dark^"266  why  lifted  easier  in  water  than  on 

Size,  4  land,  65 

Skating  swiftly  over  thin  ice,  effect  of,  27  Stove,  advantages  over  an  open  fireplace, 
Skin,  cleanliness  essential  to  the  healthy 


action  of,  237 
Sky,  why  appears  blue,  271 
Sleet,  what  is,  92 
Smoke,  what  is,  218 

why  ascends,  13 

Smoking,  how  preserves  meat,  808 
Sneezing,  what  is,  123 


Snow,  at  the  foot  of  a  wall,  why  melts  Stucco,  what  is, 


disadvantages  of,  219 

why  crackles  in  cooling,  186 

why  crackles  when  a  fire  is  kindled 

in  it,  1S6 

Stones,  why  not  suitable  for  fuel,  226 
Straw,  use  of,  in  the  Egyptian  bricks,  40 
Stripes,  effect  of,  in  dresses,  279 


rapidly,  161 
flake,  how  formed,  93 
heat  of,  how  shown,  138 


Sucker,  the  common,  72 

Suction,  height  to  which  water  may  bo 

raised  by,  98 
how    diminishes  the    darkness  of 'Suffocation,  how  occurs,  123 

night,  270  |Sugar  and  salt,  how  flavor  water,  67 

how  protects  the  surface  of  the  earth  salt,  &c.,  retard  boiling,  157 


in  winter,  92,  93 
melting  absorbs  heat,  138 
various  colors  of,  94 
what  is,  92 
why  none  in  summer,  93 

white,  93 

Soap-bubble,  origin  of  colors  in,  259 
Soap,  utility  of  in  washing,  57 
SoiC  a  bad  conductor  of  heat,  136 
effects  of  on  temperature,  107 
Solid,  what  is  a,  S 
Solution,  what  is  a,  193 

when  saturated,  193 
Sonorous  bodies,  what  are,  116 
Soot,  smell  of,  why  sometimes  noticed  in 
a  room,  216 


of,  71 

best  conductors  of,  120 
how  obstructed  by  fogs,  rain,  &c., 

119 

how  produced,  114 
louder  by  night  than  by  day,  119 
not  heard  alike  by  all  persons,  120 
velocity  of,  118 
bounds,  musical,  what  are,  120 

origin  and  transmission  of,  114 
rejection  of,  124 
transmission  of  by  solids,  117 
vibrations,  to  what  compared,  117 
vibrations  in  solids,  how  rendered 

visible,  118 


Sulphur,  product  of  when  burned,  393 

Sulphureous  acid,  303 

Sulphuric  acid,  304 

Summer,  Indian,  haziness  of,  87 

Sun,  seen  through  a  fog  appears  red,  87 
the,  a  source  of  lu-at,  132 
weight  on  the  surface  of,  19 
why  appears  large  on  the  horizon,  269 

Sun's  heat,  why  greater  in  some  portions 
of  the  earth  than  in  others,  133 

Sunbeam,  motes  floating  in,  what  arc,  ICO 

Sunset,  red,  cause  of,  86 

Surf,  what  is,  61 

Surfaces,  some,  why  brilliant,  242 
dull,  242 

Swimmers,  unskilful,  why  sink,  63 


VJound,  air  necessary  for  the  production  Swimming  why  easier  in  salt  than  in  fresh 


water.  63 
philosophy  of,  63 
Springs  in  ponds  prevent  freezing,  163 
mineral,  cause  of,  54 
origin  of,  51 

why  cool  in  summer,  150 
why  often  fail  in  dry  weather,  51 
Sprinkling  a  hot  room  how  cools  it,  198 
Squinting,  occasion  of,  268 

occasions  double  vision,  267 
Starch,  how  manufactured,  302 

may  be  converted  into  sugar,  303 
what  is,  302 

why  necessary  to  boil  before  using, 
802 


34* 


322 


INDEX. 


Stars,  shooting,  96  _ 

oacur  periodicruly,  9T 
why  not  visible   in   the  daytime, 

244    • 
Starvation,  process  of,  239 

what  is,  235 

Steam,  bulk  of,  compared  with  water,  201 
how  much    lighter    than    water, 

200 

engine,  what  is  a,  202 
high  pressure,  202 
how  used  for  cookery,  202 
invisible,  107 
its  elasticity,  201 
lighter  than  air,  68 
mechanical  force  of,  203 

illustrations  of,  203 
parts  of  a  boiler  where  first  formed, 

200 

power  of,  on  what  depends,  201 
visible   appearance   how    caused, 

200 

what  is  true,  200 
Stems  of  grain -plants,  why  hollow  tubes, 

37 

Stick  immersed  in  water,  why  seems  bro- 
ken, 254 
Still,  construction  of,  191 


Thunder,  rolling  of,  cause  of,  2S7 

storm",  places  dangerous  in,  282, 

2S3 

safest  in,  233 
what  is  a,  2SO 
varieties  of,  2S7 
what  is,  2S6 
why  heard  after  the  lightning 

is  seen,  2S7 
Tides,  cause  of,  59 

when  high  and  low,  59,  60 
Toes,  advantage  of  turning  out  the,  io 

walking,  17 
Tornadoes,  82 

phenomena  generally  attend- 
ing, 82 

Transparent  bodies,  what  are,  260 
Tree,  centre  of  gravity  in,  19 

how  discharges  a  lightning  cloud, 

2S2 

Trees  and  flowers,  how  purify  the  air,  210 
whv  covered  with  straw  in  winter, 

184 

Tropics,  rainy  and  dry  seasons  of,  109 
Troy  weight,  origin  of,  20 
Trumpet,  ear,  construction  of,  127 

speaking,  construction  of,  127 
Twilight,  cause  of~  259 


Telegraph,  influence  how  transmitted  by, 
to  convey  intelligence,  301 
magnetic,   Morse's,   principle 

of,  300,  301 
wire,  why  supported  on  glass, 

301     ' 
Telegraphic  current,  what  is  meant  by 

301 
Telescopss,  construction  and  use  of,  252, 

253 
why  enable  us  to  see 

objects,  253 
Temperature,  effect  of  the  sea  on  the,  107 

soil  on,  107 

mean  daily,  what  is,  106 

varies  with  altitude,  105 

latitude,  105 

variation,  examples  of,  105 
why  all  places  have 

same,  107 
Temples,  how  cooled  by  ether,  cologne, 

water,  &c.,  197 
Tenon,  what  is  a,  43 
Terra-cotta,  what  is,  39 
Thaw,  mo-e  chilly  than  a  frost,  183 
Thermometer,  centigrade,  191 

Fahrenheit's,  190 

Eeaumer's,  191 

indicates  difference  of  heat 

only,  192 
Thermometers  and  pyrometers,  difference 

of,  188 

construction  of,  189 
different,  190 
how  graduated,  189 
Thunder,  cause  of,  286 


Vacuum,  illustration  of,  213 

what  is  a,  71 
Valves,  pump,  93,  99 
Vapor  from  damp  linen,  what  is  it,  197 
in  a  room,  origin  of,  88 
of  the  air,  how  condensed  into  rain 

91 

Vaporization,  meaning  of,  194 
Vegetables,  why  swell  in  boiling  water, 

distant  Vegetation,  why  luxurious  on  the  margin 

of  a  river,  66 
Ventilation,  in  what  situations  is  it  perfect, 

205 

what  is,  204 

Vibration,  what  is  a,  116 
Vibrations,  sonorous,  how  illustrated,  116 
Vinegar,  what  is,  305 
not  the  Vitriol,  oil  of,  304 

Voice,  organs  of,  122 

tones  of,  how  altered,  122 
Volatile  substances,  195 
Volcanoes,  probable  cause  of,  136 


Wall,  a,  when  stands  securely,  17 
Walls,  partition,  construction  of,  to  int« 

cept  sound,  119 
Warming  and  ventilation,  204 
Water,  a  bad  conductor  of  heat,  146 

at  what  elevation  above  the  earth 

remains  frozen,  106 
air  in, 
boiled,  why  flat  and  insipid,  73 


INDEX. 


323 


Water,  composition  of,  54  I  Wheels,  carriage,  why   sometimes  take 

declivity  sufficient  to  give  fanning  lire,  189 

motion  to,  50  fore,  of    carriages,   why  smaller 

of,  why  rolls  upon  hot  iron,  than  the  hind,  44 

of  carriages,  utility  of  greasing, 

water,  different  kinds,  34 
Whitewash,  what  is,  38 
Wick  of  a  candle,  why  not  consumed, 

233 
Windpipe,  what  is  the,  122 


194 

expands  when  freezing,  181 
force  of  expansion  in  freezing,  179 
hard,  what  is,  54 

difficult  to  wash  in,  56 
bow  extinguishes  a  fire,  229 
hoAV  heated,  153 


hot,  why  hreaks  glass,  or  earthen  Windows,  why  blaze  p.t  sunset,  249 


vessels,  185 
in  freezing,  cracks  earthen   ves- 
sels, 180 

images  in,  appear  inverted,  246 
power,  33,  34 
pressure  of.  53 

how  exerted,  53 
of  mineral  matter  con- 


tained  in,  55 
running,  Avhy  slow  to  freeze,  182 
scalds  at  what  temperature,  176 
surface  of,  always  level,  49 
swells  in  boiling,  156 
temperature  ol'boiling,  135 
what  is  the  purest  natural,  55 
when  affects  lead  pipes,  310 
why  a  fluid,  54 

why  dissolves  sugar  and  salt,  57 
why  freezes  first  at  the  surface, 

182 

why  rises  in  a  pump,  101 
why  sparkles,  56 
why  will  not  dissolve  iron,  193 

Waters,  relative  purity  of,  55 

Waterspout,  what  is  a,  83 

Waves,  cause  of,  60 
spray  of,  61 
velocity  of  storm,  61 

Well,  ordinary,  why  water  collects,  57 

Wells,  artesian,  52 


why  often  covered  with  mist, 

87 

Wind,  cause  of,  75 
Winds,  force  of,  how  measured,  78 

high,  difficult  to  walk  against,  9 

always  blow,  76 

effects  of  mountains,  on  the  couira 
of,  76 

land,  generally  dry,  76 

north,  why  cold,  79 

south,  why  Avarm,  79 

regular,  77 

on" the  direction  of,  78 

trade,  77 

velocity  of,  77 
Wine,  why  sours  on  exposure  to  air,  305 
Wood,  constituents  of,  224 

green,  unprofitable  to  burn,  227 

hard  and  soft,  227 


how  preserved  from  decay,  811 

";  profitable  for  f;i 
kinds  of,   which  impart  the   least 


kinds  most  profitable  for  fuel,  227 


heat  in  burning,  227 
weight  of  a  cord  of,  227 
why  does  not  melt,  194 
why  generally  cut  in  the  winter, 

why  snaps  when  burning,  7 
Wooden  handles,  why  applied  to  cooking 
vessels,  145 


Winter,  dark  dresses  most  suitable  for,  Woollen  kettle-holders,  utility  of,  145 


172 


Teast,  what  is,  305 

Yellow,  the  color  most  visible,  272 


Weather,  action  or.  building   materials, 

48 
Weather,  animals  foretell  changes  in,  113 

moon's  influence  on,  ill 
Weight,  how  varies,  19,  20 

proportional  to  what,  19 

what  is,  19 

where  a  body  has  the  greatest, 

and  least,  20 
Weights  and  measures,  English  system  of, 

21  Zenith,  what  is  the,  269 

Weights  and  measures.  French  system  of,  Zero  point  of  thermometer,  how  dele* 

21  i     mined,  190 

Wheel,  centre  of  gravity  of,  18  ^Zodiacal  light,  97 

dished,  or  arched,  stronger  than  a 
flat,  44  i 


Woollens,  utility  of  as  protectors  against 
cold,  147 


zr. 

10- 


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IVISON,   BLAKEMAN,    TAYLOR  &  CO., 

PUBLISHERS, 

138  &  140  GRAND  STREET,  NEW  YORK. 
133  &  135  STATE  STREET,  CHICAGO. 


